Commitment Letter, dated as of January 30, 2018, with Barclays Bank PLC and JPMorgan Chase Bank, N.A

Exhibit 10.1

January 30, 2018

Seattle Genetics, Inc.

21823 30th Drive SE

Bothell, WA 98021

Project Valley

Commitment Letter

$400,000,000 364-Day Term Loan Facility

Ladies and Gentlemen:

You have advised Barclays Bank PLC (“Barclays”) and JPMorgan Chase Bank, N.A. (“JPMCB” and, together with Barclays, the “Commitment Parties” or “we” or “us”) that Seattle Genetics, Inc., a Delaware corporation (the “Borrower” or “you”), seeks financing to consummate the Transactions (such term and each other capitalized term used but not defined herein having the meanings assigned to them in Annex A hereto and the Term Sheet referred to below). This letter, including the Term Sheet, the Transaction Description attached hereto as Annex A and the Conditions Annex attached hereto as Annex C (the “Conditions Annex”), is hereinafter referred to as the “Commitment Letter”.

1.    Commitments. Upon the terms set forth in this Commitment Letter and subject to satisfaction or waiver of the conditions expressly set forth in the Conditions Annex, each of Barclays and JPMCB (in such capacities, the “Initial Lenders”) is pleased to advise you of its commitment to provide to the Borrower, on a several and not joint basis, 50% and 50%, respectively, of the aggregate principal amount of the Term Facility (the “Commitment”).

2.    Titles and Roles. Barclays and JPMCB, in each case acting alone or through or with affiliates selected by it, will act as bookrunner, lead arranger and syndication agent (in such capacities, collectively, the “Lead Arrangers”) in arranging the Term Facility. Barclays will act as the sole administrative agent (in such capacity, the “Administrative Agent”) for the Term Facility. No additional agents, co-agents, arrangers or bookrunners will be appointed and no other titles will be awarded and no other compensation will be paid (other than compensation expressly contemplated by this Commitment Letter and the fee letter dated the date hereof among the Commitment Parties and you (the “Fee Letter”)) unless you and the Lead Arrangers shall agree in writing. It is understood and agreed that Barclays will have the “left” and “highest” placement in any and all marketing materials or other documentation used in connection with the Term Facility and shall hold the leading role and responsibilities conventionally associated with such placement, including maintaining sole physical books for the Term Facility. You agree that JPMCB may perform its responsibilities hereunder through its affiliate, J.P. Morgan Securities LLC.

3.    Conditions to Commitment. The Commitment and undertakings of the Commitment Parties hereunder are subject solely to the satisfaction or waiver of the conditions precedent set forth in the Conditions Annex.

Notwithstanding anything in this Commitment Letter, the Fee Letter or the Financing Documentation (as defined in the Conditions Annex) or any other letter agreement or other undertaking concerning the financing of the Transactions to the contrary, (a) the only representations and warranties the accuracy of which shall be a condition to the availability of the Term Facility on the Closing Date, shall be (i) such of the representations made by the Target with respect to the Target or its businesses in the Acquisition Agreement as are material to the interests of the Lenders, but only to the extent that you or any of your affiliates have the right (taking into account any applicable cure periods) to terminate your or such affiliate’s obligations under the Acquisition Agreement or otherwise decline to close the Acquisition (in each case, in accordance with the terms of the Acquisition Agreement) as a result of a breach of any such representations and warranties in the Acquisition Agreement or any such representation or warranty not being accurate (the “Specified Acquisition Agreement Representations”) and (ii) the Specified Representations (as defined below) and (b) the terms of the Financing Documentation shall be in a form such that they do not impair the availability of the Term Facility on the Closing Date if the conditions set forth in Annex B are satisfied or waived by the Lenders (it is understood that, to the extent any guaranty or lien search or security interest in the intended Collateral (other than (x) in the certificated equity securities of any material wholly owned U.S. domestic subsidiaries of the Borrower (other than the Target and its subsidiaries) and related stock powers to the extent constituting Collateral, (y) Uniform Commercial Code (“UCC”) lien searches in an entity’s jurisdiction of organization for entities organized in the United States and (y) any Collateral the security interest in which may be perfected by the filing of a UCC financing statement for entities organized in the United States) is not or cannot be provided or perfected in accordance with the Term Sheet on the Closing Date after your use of commercially reasonable efforts to do so or without undue burden or expense, then the provision of any such guaranty or lien search and/or the perfection of security interests in such Collateral shall not constitute a condition precedent to the availability of the Term Loans on the Closing Date, but shall be required to be delivered and/or perfected within 60 days after the Closing Date (in each case, subject to extensions to be reasonably agreed upon by the Administrative Agent)). For purposes hereof, “Specified Representations” means the representations and warranties of the Loan Parties set forth in the Term Loan Documentation relating to corporate or other organizational existence and good standing in such Loan Party’s jurisdiction of organization; power and authority, due authorization, execution and delivery and enforceability, in each case, relating to the Loan Parties’ entering into and performance of the Financing Documentation; enforceability of the Financing Documentation against the Loan Parties; no conflicts with or consents required under the Loan Parties’ organizational documents relating to entering into and performance of the Financing Documentation; solvency as of the Closing Date (after giving effect to the Transactions, with solvency being determined in a manner consistent with Exhibit D to this Commitment Letter) of the Loan Parties on a consolidated basis; Federal Reserve margin regulations; the Investment Company Act; use of proceeds in violation of the PATRIOT Act, OFAC and FCPA. This paragraph, and the provisions herein, shall be referred to as the “Limited Conditionality Provision”.

4.    Syndication.

(a)    The Lead Arrangers reserve the right, both prior to and after the Closing Date, to secure commitments for the Term Facility from a syndicate of banks, financial institutions and other entities reasonably acceptable to you (such financial institutions and other entities committing to the Term Facility, including the Initial Lenders, the “Lenders”) (it is understood that the Lead Arrangers will not syndicate to (x) any competitor identified in writing to the Lead Arrangers or (y) any affiliate of a competitor of the Borrower or the Target that is either (i) clearly identifiable on the basis of name or (ii) identified in writing to the Lead Arrangers (other than any such affiliate that is affiliated with a financial investor in such person and that is not itself an operating company or otherwise an affiliate of an operating company so long as such affiliate is a bona fide debt fund (a “Disqualified Lender”); provided, that no addition to the list of Disqualified Lenders shall apply retroactively to disqualify any parties that

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have previously acquired an assignment or participation interest in the Term Facility, but such person shall be disqualified from purchasing future assignments and participations)) upon the terms and subject to the conditions set forth in this Commitment Letter. Until the date that is 60 days following the Closing Date (the “Syndication Date”), you agree to assist the Lead Arrangers actively in achieving a syndication of the Term Facility that is satisfactory to the Lead Arrangers and you. To assist the Lead Arrangers in their syndication efforts, you agree that you will, and will use your commercially reasonable efforts to cause your representatives and advisors to, (i) provide promptly to the Commitment Parties upon request all customary information reasonably requested by the Lead Arrangers to assist the Lead Arrangers to complete the syndication, (ii) make your senior management available to prospective Lenders at times and places to be mutually agreed that will not interfere with the normal operation of your business, (iii) host, with the Lead Arrangers, one or more meetings or calls with prospective Lenders at mutually agreed times and locations (provided in no event shall you be required to host more than one bank meeting), (iv) assist, and use your commercially reasonable efforts to cause your advisors to assist, the Lead Arrangers in the preparation of one or more customary confidential information memoranda and other customary marketing materials to be used in connection with the syndication and (v) your ensuring that prior to the Syndication Date (and using your commercially reasonable efforts to cause your representatives and advisors to ensure) there will be no competing issues, offerings, placements, arrangements or syndications of debt or equity securities or commercial bank or other credit facilities by or on behalf of you or your subsidiaries or the Target or its subsidiaries being offered, placed or arranged (other than the Term Facility, any Securities Issuance and any Refinancing) without the written consent of the Lead Arrangers, unless such issuance, offering, placement, arrangement or syndication could not reasonably be expected to materially impair the primary syndication of the Term Facility (it being understood that indebtedness incurred in the ordinary course of business of the Borrower and its subsidiaries for capital expenditures and working capital purposes will not materially impair the primary syndication of the Term Facility). For the avoidance of doubt, you will not be required to provide any information to the extent that the provision thereof would violate any attorney-client privilege, law, rule or regulation, or any obligation of confidentiality from a third party binding on you, the Target or any of your or its respective affiliates (so long as such confidentiality obligation was not entered into in contemplation of the Transactions); provided that you shall use commercially reasonable efforts to obtain the relevant consents under such obligations of confidentiality to allow for the provision of such information to the extent reasonably requested by the Lead Arrangers; provided, further, that you will inform the Lead Arrangers, in advance and to the extent legally permitted, that you are withholding any information pursuant to the foregoing. Your obligations under this Commitment Letter to use commercially reasonable efforts to cause the Target or members of its management to take (or to refrain from taking) any action shall be subject to any applicable limitation on your rights as set forth in the Acquisition Agreement.

(b)    The Lead Arrangers and/or one or more of their respective affiliates will manage all aspects of the syndication of the Term Facility (in consultation with you), including decisions as to the selection and number of potential Lenders to be approached, when they will be approached, whose commitments will be accepted, subject to your consent (with your consent not to be unreasonably withheld or delayed), any titles offered to the Lenders and the final allocations of the commitments and any related fees among the Lenders, and the Lead Arrangers will exclusively perform all functions and exercise all authority as is customarily performed and exercised in such capacities. Notwithstanding the Lead Arrangers’ rights to syndicate the Term Facility and receive commitments with respect thereto, unless otherwise agreed to by you, (i) none of the Initial Lenders shall not be relieved or released from its obligations hereunder (including its obligation to fund the Term Facility on the Closing Date) in connection with any syndication, assignment or participation in the Term Facility, including its Commitment, until the funding under the Term Facility has occurred on the Closing Date, (ii) no assignment by an Initial Lender shall become effective with respect to all or any portion of such Initial Lender’s Commitment until the funding of the Term Facility (except to the extent that the Borrower has

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consummated a Securities Issuance and/or Refinancing and proceeds thereof are available on or prior to the Closing Date in lieu of the Term Facility or a portion thereof), (iii) the Initial Lenders shall, in all cases, retain, in the aggregate, 50.1% of the Commitment, and (iv) unless you and we agree in writing, the Initial Lenders shall retain exclusive control over all rights and obligations with respect to its Commitment in respect of the Term Facility, including all rights with respect to consents, modifications, supplements, waivers and amendments, until the Closing Date has occurred. Notwithstanding the foregoing, the Commitment Parties will not syndicate or otherwise assign, novate or transfer any portion of a commitment hereunder or under the Term Facility, or participate or novate any portion of a commitment hereunder or under the Term Facility, to any Disqualified Lender without the prior written consent of the Borrower. Without limiting your obligations to assist with the syndication efforts as set forth herein, it is understood that the Commitment hereunder is not conditioned upon the commencement or completion of the syndication of, or receipt of commitments in respect of, the Term Facility and in no event shall either the successful completion of the syndication of the Term Facility or compliance with the Commitment Letter constitute a condition to the availability of the Term Facility on the Closing Date.

5.    Information.

(a)    You represent, warrant and covenant that (to the best of your knowledge, insofar as it relates to the Target and its subsidiaries) (i) all written information and written data (other than the Projections, as defined below, other forward-looking information, estimates and information of a general economic or general industry nature) concerning the Borrower, its subsidiaries, the Target, its subsidiaries and any aspect of the Transactions that has been or will be made available to the Commitment Parties or the Lenders by you or any of your or their representatives, subsidiaries or affiliates (or on your or their behalf) (the “Information”), when taken as a whole (after giving effect to any supplements or updates), (x) is and will be true, complete and correct in all material respects and (y) does not, and in the case of Information made available after the date hereof, will not contain any untrue statement of a material fact or omit to state a material fact necessary in order to make the statements contained therein, in light of the circumstances under which they were made, not materially misleading and (ii) all financial projections concerning the Borrower and its subsidiaries or the Target and its subsidiaries, taking into account the consummation of the Transactions, that have been or will be made available to any of the Commitment Parties or the Lenders by you or any of your representatives, subsidiaries or affiliates (or on your or their behalf) (the “Projections”) have been and will be prepared in good faith with a reasonable basis for the assumptions and the conclusions reached therein on the date provided (it being understood that (w) the Projections are as to future events and are not to be viewed as facts, (x) the Projections are subject to significant uncertainties and contingencies, many of which are beyond your control, (y) no assurance can be given that any particular Projections will be realized and (z) actual results during the period or periods covered by any such Projections may differ significantly from the projected results and such differences may be material). You agree that if, at any time prior to the Syndication Date, you become aware that any of the representations and warranties contained in the preceding sentence would be incorrect in any material respect if the Information and Projections were being furnished, and such representations were being made, at such time, then you will promptly supplement (or use commercially reasonable efforts to supplement, in the case of Information relating to the Target, if previously prepared and available) the Information and the Projections so that such representations are correct in all material respects under those circumstances. We will be entitled to use and rely upon, without responsibility to verify independently, the Information and the Projections. You acknowledge that we may share with any of our affiliates for purposes of providing services under this Commitment Letter (it being understood that such affiliates will be subject to the confidentiality agreements between you and us), and such affiliates may share with the Commitment Parties, any information related to you, the Target, or any of your or the Target’s subsidiaries or affiliates (including, without limitation, in each case, information relating to creditworthiness) and the transactions contemplated hereby.

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(b)    You acknowledge that (i) the Commitment Parties will make available, on your behalf, the Information, Projections and other marketing materials and presentations, including the confidential information memoranda (collectively, the “Informational Materials”), to the potential Lenders by posting the Informational Materials on SyndTrak Online or by other similar electronic means (collectively, the “Electronic Means”) and (ii) certain prospective Lenders may be “public side” (i.e., lenders that have personnel that do not wish to receive material non-public information (within the meaning of the United States federal securities laws, “MNPI”) with respect to the Borrower, the Target or your or its subsidiaries or affiliates or any of your or their respective securities, and who may be engaged in investment and other market-related activities with respect to such entities’ securities (such Lenders, “Public Lenders”). At the request of the Lead Arrangers, (A) you will assist, and use your commercially reasonable efforts to cause your advisors, and to the extent possible using commercially reasonable efforts, appropriate representatives of the Target to assist (to the extent not in contravention of the Acquisition Agreement), the Lead Arrangers in the preparation of Informational Materials to be used in connection with the syndication of the Term Facility to Public Lenders, which will not contain MNPI (the “Public Informational Materials”) and (B) at the request of the Lead Arrangers you will identify and conspicuously mark any Public Informational Materials “PUBLIC”. Notwithstanding the foregoing, you agree that the Commitment Parties may distribute the following documents to all prospective Lenders (including the Public Lenders) (other than Disqualified Lenders) on your behalf, unless you advise the Commitment Parties in writing (including by email) within a reasonable time prior to their intended distributions that such material should not be distributed to Public Lenders: (w) administrative materials for prospective Lenders such as lender meeting invitations and funding and closing memoranda, (x) notifications of changes in the terms of the Term Facility, (y) historical financial information regarding the Borrower and its subsidiaries (other than the Projections) and the Target and its subsidiaries that have been publicly disclosed and (z) drafts and final versions of the Term Sheet and the Financing Documentation. If you advise us in writing (including by email) that any of the foregoing items (other than the Financing Documentation) should not be distributed to Public Lenders, then the Commitment Parties will not distribute such materials to Public Lenders without further discussions with you. Before distribution of any Informational Materials to prospective Lenders, you shall provide us with a customary letter authorizing the dissemination of the Informational Materials and confirming the accuracy and completeness in all material respects of the information contained therein and, in the case of Public Informational Materials, confirming the absence of MNPI therefrom. In addition, the Information Materials shall (I) exculpate you with respect to any liability related to the misuse of the contents of such Information Materials or any related offering and marketing materials by the recipients thereof and (II) exculpate us with respect to any liability related to the use or misuse of the contents of such Information Materials or any related offering and marketing materials by the recipients thereof.

6.    Indemnification. You agree to indemnify and hold harmless each Commitment Party and each of its affiliates and their respective directors, officers, employees, partners, representatives, advisors and agents and each of their respective heirs, successors and assigns (each, an “Indemnified Party”) from and against any and all actions, suits, losses, claims, damages, penalties, liabilities and reasonable and documented out-of-pocket expenses of any kind or nature (including legal expenses), joint or several, to which such Indemnified Party may become subject or that may be incurred or asserted or awarded against such Indemnified Party, in each case arising out of or in connection with or by reason of (including, without limitation, in connection with any investigation, litigation or proceeding or preparation of a defense in connection therewith) (a) any matters contemplated by this Commitment Letter, the Transactions or any related transaction (including, without limitation, the execution and delivery of this Commitment Letter, the Financing Documentation, or the definitive documentation for any Securities Issuance and/or Refinancing issued or incurred for the purpose of refinancing or reducing the Commitment with respect to all or a portion of the Term Facility and the closing of the Transactions) or (b) the use or the contemplated use of the proceeds of the Term Facility, and will reimburse each Indemnified Party for all out-of-pocket expenses (but limited, in the case of legal fees and expenses, to

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the reasonable and documented out-of-pocket fees, disbursements and other charges of one counsel to all Indemnified Parties (taken as a whole) and, if reasonably necessary, a single local counsel for all Indemnified Parties (taken as a whole) in each relevant jurisdiction and with respect to each relevant specialty, and in the case of an actual or perceived conflict of interest, one additional counsel in each relevant jurisdiction to the affected Indemnified Parties similarly situated and taken as a whole) on written demand as they are incurred in connection with any of the foregoing; provided that you will not have to indemnify any Indemnified Party against (A) any claim, loss, penalty, damage, liability or expense to the extent found by a final, non-appealable judgment of a court of competent jurisdiction to have resulted from (i) the gross negligence, bad faith or willful misconduct of such Indemnified Party, (ii) a material breach of obligations under the Commitment Letter or the Financing Documentation by such Indemnified Party or (iii) any dispute solely among the Indemnified Parties (not arising as a result of any act or omission by the Borrower or any of its subsidiaries or affiliates) other than any claim, action, suit, inquiry, litigation, investigation or other proceeding brought by or against any such Indemnified Party in its capacity as agent or arranger, or (B) any settlement entered into by such Indemnified Party without your written consent, but if settled with your written consent (such consent not to be unreasonably withheld, conditioned or delayed) or if there is a judgment in any such action, suit, proceeding or claim, you agree to indemnify and hold harmless each Indemnified Party from and against any and all losses, claims, damages, liabilities or expenses by reason of such settlement or judgment in accordance with the provisions of this paragraph. In the case of an investigation, litigation or proceeding to which the indemnity in this paragraph applies, such indemnity shall be effective whether or not such investigation, litigation or proceeding is brought by you, your equity holders or creditors or an Indemnified Party, whether or not an Indemnified Party is otherwise a party thereto and whether or not the transactions contemplated hereby are consummated. No Indemnified Party will be liable to you, your affiliates or any other person for any damages arising from the use by others of Informational Materials or other materials obtained by Electronic Means, except to the extent that your damages are found in a final non-appealable judgment by a court of competent jurisdiction to have resulted from the gross negligence or willful misconduct of such Indemnified Party. You shall not, without the prior written consent of each Indemnified Party affected thereby (which consent shall not be unreasonably conditioned, withheld or delayed), settle any threatened or pending claim or action that would give rise to the right of any Indemnified Party to claim indemnification hereunder unless such settlement (x) includes a full and unconditional release of all liabilities arising out of such claim or action against such Indemnified Party, (y) does not include any statement as to or an admission of fault, culpability or failure to act by or on behalf of such Indemnified Party and (z) requires no action on the part of the Indemnified Party other than its consent (which consent shall not be unreasonably conditioned, withheld or delayed).

Neither you nor we nor any other Indemnified Party will be responsible or liable for any indirect, special, punitive or consequential damages which may be alleged as a result of the Acquisition, this Commitment Letter, the Fee Letter, the Term Facility, any Securities Issuance, any Refinancing, the Transactions or any related transaction contemplated hereby or thereby or any use or intended use of the proceeds of any financing; provided that nothing contained in this sentence shall limit your indemnity or reimbursement obligations to the extent set forth above in this Section 6 in respect of any losses, disputes, claims, damages, liabilities and expenses incurred or paid by an Indemnified Person to a third party that are otherwise required to be indemnified in accordance with this Section 6. You also agree that no Indemnified Party will have any liability (whether direct or indirect, in contract or tort, or otherwise) to you or your affiliates or to your or their respective equity holders or creditors arising out of, related to or in connection with any aspect of the transactions contemplated hereby, except to the extent such liability to you is determined in a final, non-appealable judgment by a court of competent jurisdiction to have resulted from (i) the gross negligence or willful misconduct of such Indemnified Party or (ii) a material breach of obligations under the Commitment Letter or the Financing Documentation by such Indemnified Party.

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7.    Fees. As consideration for the commitments and agreements of the Commitment Parties hereunder, you agree to cause to be paid the nonrefundable fees described in the Fee Letter on the terms and subject to the conditions set forth therein.

8.    Confidentiality.

(a)    This Commitment Letter and the Fee Letter (collectively, the “Commitment Documents”) and the existence and contents hereof and thereof are confidential and may not be disclosed, directly or indirectly, by you in whole or in part to any person without our prior written consent, except for disclosure (i) hereof or thereof on a confidential basis to your directors, officers, employees, accountants, attorneys and other professional advisors who have been advised of their obligation to maintain the confidentiality of the Commitment Documents for the purpose of evaluating, negotiating or entering into the Transactions, (ii) as otherwise required by applicable law, rule or regulation or compulsory legal process or pursuant to a subpoena (in which case, you agree, to the extent permitted by law, to inform us promptly in advance thereof), (iii) on a confidential basis to the Target and its subsidiaries, their respective officers, directors, employees, independent auditors, legal counsel and other advisors (provided that any information relating to pricing, fees and expenses has been redacted in a manner reasonably acceptable to us), (iv) of this Commitment Letter, but not the Fee Letter, in any required filings with the Securities and Exchange Commission and any other applicable regulatory authorities and stock exchanges or in any prospectus or other offering memorandum relating to the Term Facility, any Securities Issuance or any Refinancing, (v) of the Term Sheet to any ratings agency or any prospective Lenders in connection with the Transactions, (vi) of the aggregate fee amounts contained in the Fee Letter as part of projections, pro forma information or as part of a generic disclosure of aggregate sources and uses related to fee amounts applicable to the Transactions to the extent customary or required in offering and marketing materials for the Term Facility and/or any Securities Issuance and/or any Refinancing or in any public release or filing relating to the Transactions, (vii) pursuant to the order of any court or administrative agency in any pending legal, judicial or administrative proceeding, or otherwise as required by applicable law, compulsory legal process or to the extent requested or required by governmental and/or regulatory authorities, in each case, based on the advice of your legal counsel (in which case you agree, to the extent practicable and not prohibited by applicable law, to inform us promptly thereof), and (viii) in connection with the exercise of any remedy or enforcement of any right under this Commitment Letter and the Fee Letter. The Commitment Parties shall be permitted to use information related to the syndication and arrangement of the Term Facility (including your name and company logo) in connection with obtaining a CUSIP number, marketing, press releases or other transactional announcements or updates provided to investor or trade publications, subject to (i) confidentiality obligations or disclosure restrictions reasonably requested by you and (ii) your and the Target’s name and company logo being used solely in a manner that is not intended to, nor reasonably likely to, harm or disparage you, the Target or either of your subsidiaries. The confidentiality provisions of this paragraph (a) with respect to the Borrower (other than with respect to the Fee Letter) shall automatically terminate on the date that is two (2) years from the date of this Commitment Letter.

(b)    We agree to use all non-public information provided to us by or on behalf of the Borrower hereunder solely for the purpose of providing the services which are the subject of this Commitment Letter and to treat all such information confidentially; provided, that nothing herein shall prevent a Commitment Party from disclosing any such information (i) to any Lenders or participants or prospective Lenders or participants or any direct or indirect contractual counterparties (or prospective counterparties) to any swap or derivative transaction relating to the Borrower and its obligations under the Term Facility, in each case other than Disqualified Lender, (ii) as otherwise required by applicable law, rule or regulation or compulsory legal process or pursuant to a subpoena (in which case, we agree, to the extent permitted by law, to inform you promptly in advance thereof), (iii) upon the request or demand of any regulatory authority having jurisdiction over such Commitment Party or its affiliates (in which case

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such Commitment Party shall, except with respect to any audit or examination conducted by bank accountants or any governmental bank regulatory authority exercising examination or regulatory authority, promptly notify you, in advance, to the extent practicably and lawfully permitted to do so), (iv) to the employees, legal counsel, independent auditors, professionals and other experts or agents of such Commitment Party who are informed of the confidential nature of such information and are or have been advised of their obligation to keep information of this type confidential, (v) to any of its respective affiliates solely in connection with the Transactions, (vi) to the extent any such information becomes publicly available other than by reason of disclosure by such Commitment Party or its affiliates in breach of this Commitment Letter, (vii) to the extent that such information is received by such Commitment Party from a third party that is not to such Commitment Party’s knowledge subject to confidentiality obligations to you or the Borrower, (viii) to the extent that such information is independently developed by such Commitment Party without the use of confidential information, (ix) to ratings agencies in connection with the Transactions and (x) for purposes of establishing a “due diligence” defense; provided, further that the disclosure of any such information to any Lenders or prospective Lenders or participants or prospective participants referred to above shall be made subject to the acknowledgment and acceptance by such Lender or prospective Lender or participant or prospective participant that such information is being disseminated on a confidential basis (on substantially the terms set forth in this paragraph or as is otherwise reasonably acceptable to you and the Commitment Parties, including, without limitation, as agreed in any confidential information memorandum or other marketing materials) in accordance with the standard syndication processes of the Commitment Parties or customary market standards for dissemination of such type of information. The provisions of this paragraph (b) with respect to the Commitment Parties shall automatically be superseded by the confidentiality provisions to the extent covered in the Financing Documentation and shall in any event automatically terminate two (2) years following the date of this Commitment Letter.

(c)    The Commitment Parties hereby notify you that pursuant to the requirements of the USA PATRIOT Act, Title III of Pub. L. 107-56 (signed into law October 26, 2001) (the “PATRIOT Act”), it and each Lender may be required to obtain, verify and record information that identifies you, which information includes your name, address, tax identification number and other information that will allow the Commitment Parties and the other Lenders to identify you in accordance with the PATRIOT Act. This notice is given in accordance with the requirements of the PATRIOT Act and is effective for each of us and the Lenders.

9.    Other Services.

(a)    Nothing contained herein shall limit or preclude the Commitment Parties or any of their respective affiliates from carrying on any business with, providing banking or other financial services to, or from participating in any capacity, including as an equity investor, in any party whatsoever, including, without limitation, any competitor, supplier or customer of you, the Target, or any of your or its affiliates, or any other party that may have interests different than or adverse to such parties.

(b)    You acknowledge that the Lead Arrangers and their respective affiliates (the term “Lead Arranger” as used in this section being understood to include such affiliates) (i) may be providing debt financing, equity capital or other services (including financial advisory services) to other entities and persons with which you, the Target, or your or its affiliates or subsidiaries may have conflicting interests regarding the Transactions and otherwise, (ii) may act, without violation of its contractual obligations to you, as it deems appropriate with respect to such other entities or persons, and (iii) have no obligation in connection with the Transactions to use, or to furnish to you, the Target, or your affiliates or subsidiaries, confidential information obtained from other entities or persons. In particular, you acknowledge that the Lead Arrangers may possess information about the Target, the Acquisition and other potential purchasers and their respective strategies and bids, but the Lead Arrangers have no obligation to furnish to you such information.

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(c)    In connection with all aspects of the Transactions, you acknowledge and agree that: (i) the Term Facility and any related arranging or other services contemplated in this Commitment Letter constitute an arm’s-length commercial transaction between you and your affiliates, on the one hand, and the Commitment Parties, on the other hand, and you are capable of evaluating and understanding and understand and accept the terms, risks and conditions of the Transactions, (ii) in connection with the process leading to the Transactions, each Commitment Party is and has been acting solely as a principal and not as a financial advisor, agent or fiduciary, for you or any of your management, affiliates, equity holders, directors, officers, employees, creditors or any other party, (iii) except as described in subsection (d) below, neither of the Commitment Parties nor any of their respective affiliates thereof has assumed or will assume an advisory, agency or fiduciary responsibility in your or your affiliates’ favor with respect to any of the Transactions or the process leading thereto (irrespective of whether such Commitment Party or any of its affiliates has advised or is currently advising you or your affiliates on other matters) and the Commitment Parties have no obligation to you or your affiliates with respect to the Transactions except those obligations expressly set forth in the Commitment Documents, (iv) the Commitment Parties and their respective affiliates may be engaged in a broad range of transactions that involve interests that differ from yours and those of your affiliates and the Commitment Parties shall have no obligation to disclose any of such interests, and (v) the Commitment Parties have not provided any legal, accounting, regulatory or tax advice with respect to any of the Transactions and you have consulted your own legal, accounting, regulatory and tax advisors to the extent you have deemed appropriate. You hereby waive and release, to the fullest extent permitted by law, any claims that you may have against the Commitment Parties or any of their respective affiliates with respect to any breach or alleged breach of agency or fiduciary duty.

(d)    In addition, please note that each of Barclays Capital Inc. and J.P. Morgan Securities LLC has been retained by you as financial advisor (in such capacity each, the “M&A Advisor”) in connection with the Acquisition. You agree to such retention, and further agree not to assert any claim you might allege based on any actual or potential conflicts of interest that might be asserted to arise or result from, on the one hand, the engagement of the M&A Advisor, and on the other hand, our and our affiliates’ relationships with you as described and referred to herein.

10.    Acceptance/Expiration/Termination of Commitments.

(a)    This Commitment Letter and the Commitment of the Initial Lenders and the undertakings of the Lead Arrangers set forth herein shall automatically terminate at 11:59 p.m. (Eastern Time) on January 30, 2018 (the “Acceptance Deadline”), without further action or notice unless signed counterparts of this Commitment Letter and the Fee Letter shall have been delivered to counsel to the Lead Arrangers by such time.

(b)    In the event this Commitment Letter is accepted by you as provided above, the Commitment of the Initial Lenders, the agreements of the Commitment Parties and the undertakings of the Lead Arrangers set forth herein will automatically terminate without further action or notice upon the earliest to occur of (i) consummation of the Acquisition (with or without the use of the Term Facility), (ii) termination of the Acquisition Agreement in accordance with its terms, or your written notice of abandonment of the Acquisition, (iii) the consummation of one or more Securities Issuances and/or Refinancings for net cash proceeds equal to or in excess of the initial aggregate principal amount of the Commitment and (iv) June 30, 2018, in each case, unless the closing of the Term Facility has been consummated on or before such date on the terms and subject to the conditions set forth herein.

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(c)    You may terminate this Commitment Letter, the Commitment of the Initial Lenders, the agreements of the Commitment Parties and the undertakings of the Lead Arrangers set forth herein in full (but not in part) at any time in your sole and absolute discretion subject to the survival provisions set forth in Section 11 below.

11.    Survival. The sections of this Commitment Letter and the Fee Letter relating to any compensation (if and as applicable), Indemnification, Expenses, Confidentiality, Other Services, Survival and Governing Law shall survive any termination or expiration of this Commitment Letter, the Commitment of the Initial Lenders, the agreement of the Commitment Parties or the undertakings of the Lead Arrangers set forth herein (regardless of whether definitive Financing Documentation is executed and delivered), and the sections relating to Syndication and Information shall survive until the completion of the syndication of the Term Facility; provided that your obligations under this Commitment Letter (other than your obligations with respect to the sections of this Commitment Letter relating to Syndication, Information, Confidentiality, Other Services, Survival and Governing Law) shall automatically terminate and be superseded by the provisions of the Financing Documentation upon the funding thereunder, to the extent covered thereby, and you shall be released from all liability in connection therewith at such time.

12.    Governing Law. THIS COMMITMENT LETTER AND THE FEE LETTER, AND ANY CLAIM, CONTROVERSY OR DISPUTE ARISING UNDER OR RELATED THERETO (INCLUDING, WITHOUT LIMITATION, ANY CLAIMS SOUNDING IN CONTRACT LAW OR TORT LAW ARISING OUT OF THE SUBJECT MATTER HEREOF OR THEREOF), SHALL BE GOVERNED BY, AND CONSTRUED IN ACCORDANCE WITH, THE LAWS OF THE STATE OF NEW YORK (INCLUDING SECTION 5-1401 AND SECTION 5-1402 OF THE GENERAL OBLIGATIONS LAW OF THE STATE OF NEW YORK), WITHOUT REFERENCE TO ANY OTHER CONFLICTS OR CHOICE OF LAW PRINCIPLES THEREOF; PROVIDED THAT, NOTWITHSTANDING THE FOREGOING TO THE CONTRARY, IT IS UNDERSTOOD AND AGREED THAT ANY DETERMINATIONS AS TO (X) THE ACCURACY OF THE SPECIFIED ACQUISITION AGREEMENT REPRESENTATIONS AND WHETHER ANY SPECIFIED ACQUISITION AGREEMENT REPRESENTATIONS HAVE BEEN BREACHED AND WHETHER YOU (OR YOUR AFFILIATES) HAVE THE RIGHT TO TERMINATE YOUR (OR THEIR) OBLIGATIONS UNDER THE ACQUISITION AGREEMENT OR TO DECLINE TO CONSUMMATE THE ACQUISITION AND (Y) WHETHER THE ACQUISITION HAS BEEN CONSUMMATED IN ACCORDANCE WITH THE TERMS OF THE ACQUISITION AGREEMENT SHALL, IN EACH CASE BE GOVERNED BY THE LAWS OF THE STATE OF DELAWARE. THE PARTIES HEREBY WAIVE ANY RIGHT TO TRIAL BY JURY WITH RESPECT TO ANY CLAIM OR ACTION ARISING OUT OF THIS COMMITMENT LETTER OR THE FEE LETTER. With respect to any suit, action or proceeding arising in respect of this Commitment Letter or the Fee Letter or any of the matters contemplated hereby or thereby, the parties hereto hereby irrevocably and unconditionally submit to the exclusive jurisdiction of any state or federal court located in the Borough of Manhattan, and irrevocably and unconditionally waive any objection to the laying of venue of such suit, action or proceeding brought in such court and any claim that such suit, action or proceeding has been brought in an inconvenient forum. The parties hereto hereby agree that service of any process, summons, notice or document by registered mail addressed to you or the Commitment Parties will be effective service of process against such party for any action or proceeding relating to any such dispute. A final judgment in any such action or proceeding may be enforced in any other courts with jurisdiction over you or the Commitment Parties.

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13.    Miscellaneous. This Commitment Letter and the Fee Letter embody the entire agreement among the Commitment Parties and you and your affiliates with respect to the specific matters set forth above and supersede all prior agreements and understandings relating to the subject matter hereof. No person has been authorized by the Commitment Parties to make any oral or written statements inconsistent with this Commitment Letter or the Fee Letter. This Commitment Letter and the Fee Letter shall not be assignable by (x) you without the prior written consent of the Commitment Parties or (y) the Commitment Parties (except as provided in Section 4(b)) without your prior written consent, and any purported assignment without such consent shall be void. This Commitment Letter and the Fee Letter are not intended to benefit or create any rights in favor of any person other than the parties hereto and thereto, the Lenders and, with respect to indemnification, each Indemnified Party. This Commitment Letter and the Fee Letter may be executed in separate counterparts and delivery of an executed signature page of this Commitment Letter and the Fee Letter by facsimile or electronic mail shall be effective as delivery of manually executed counterpart hereof; provided that, upon the request of any party hereto or thereto, such facsimile transmission or electronic mail transmission shall be promptly followed by the original thereof. This Commitment Letter and the Fee Letter may only be amended, modified or superseded by an agreement in writing signed by each of you and the Commitment Parties.

14.    Binding Agreement. Each of the parties agrees that this Commitment Letter and the Fee Letter, if accepted by you as provided above, are binding and enforceable agreements with respect to the subject matter contained herein and therein, including an agreement by the parties hereto to negotiate in good faith the Financing Documentation in a manner consistent with this Commitment Letter, it being acknowledged and agreed that the effectiveness and funding of the Term Facility is subject to the conditions precedent set forth in the Conditions Annex; provided, that nothing contained in this Commitment Letter or the Fee Letter obligates you or any of your affiliates to consummate the Transactions or to draw upon all or any portion of the Term Facility.

[Signature Pages Follow]

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If you are in agreement with the foregoing, please indicate acceptance of the terms hereof by signing the enclosed counterpart of this Commitment Letter and returning it to counsel to the Lead Arrangers, together with an executed counterpart of the Fee Letter, by no later than the Acceptance Deadline.

[Commitment Letter Signature Page]

Agreed to and accepted as of the date first

above written:

[Commitment Letter Signature Page]

Annex A

$400,000,000 364-DAY TERM LOAN FACILITY

TRANSACTION DESCRIPTION

Capitalized terms not otherwise defined herein shall have the meanings assigned to them in the Commitment Letter to which this Transaction Description is attached.

The Borrower, directly or through one or more wholly owned subsidiaries, intends to acquire (the “Acquisition”) all of the equity interests of Cascadian Therapeutics, Inc. a Delaware corporation (the “Target”), pursuant to that certain Agreement and Plan of Merger dated as of January 30, 2018 by and among the Borrower, Valley Acquisition Sub, Inc., Delaware corporation and a wholly-owned subsidiary of the Borrower, and the Target (including all schedules and exhibits thereto, the “Acquisition Agreement”).

In connection with the foregoing, it is intended that:

(a)    The Acquisition will be consummated in all material respects pursuant to the terms and conditions of the Acquisition Agreement. The date on which the Acquisition is consummated is referred to as the “Closing Date”.

(b)    The Borrower will borrow on the Closing Date under a 364-day Term Loan Facility (the “Term Facility”) up to an aggregate principal amount of the lesser of (x) $400,000,000 and (y) 1.3333 multiplied by the Minimum Liquidity Amount (as defined in the Summary of Proposed Terms and Conditions attached to the Commitment Letter as Annex B (the “Term Sheet”)) to fund the Acquisition and pay related fees and expenses, which amounts shall be reduced on or prior to the Closing Date, by the net cash proceeds from (i) any public or private issuance and/or sale of shares of the Borrower or one of its subsidiaries (including, but not limited to, common equity, preferred equity, securities convertible or exchangeable into or exercisable for equity securities, other equity-linked securities or hybrid debt-equity securities or similar instruments or transactions) or debt securities (any of the foregoing items, the “Takeout Securities”; the issuance by the Borrower or one of its subsidiaries of any such Takeout Securities, a “Securities Issuance”) and/or (ii) borrowings under bank or other debt facilities (including, but not limited to, term loans, mezzanine debt or other subordinated debt) (any of the foregoing items, the “Takeout Debt Facilities”; the incurrence by the Borrower or one of its subsidiaries of any such Takeout Debt Facilities, a “Refinancing”), in each case of the foregoing clauses (i) and (ii), issued or incurred after the date hereof and on or prior to the Closing Date and excluding (A) indebtedness incurred in the ordinary course of business for working capital and capital expenditures purposes and (B) issuances pursuant to employee compensation plans, employee benefit plans, employee incentive plans and retirement plans or issued as compensation to officers and/or non-employee directors.

(c)    Fees, commissions and expenses in connection with the foregoing (the “Transaction Costs”) will be paid.

The transactions described above are collectively referred to herein as the “Transactions”. Except as the context otherwise requires, references to the “Borrower and its subsidiaries” will include any entity formed by the Borrower for purposes of acquiring the Target and shall give effect to the Transactions.

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ANNEX B

$400,000,000

364-DAY TERM LOAN FACILITY

SUMMARY OF PROPOSED TERMS AND CONDITIONS

Capitalized terms not otherwise defined herein shall have the meanings assigned to them in the Commitment Letter to which this Summary of Proposed Terms and Conditions is attached.

Annex B – Term Facility Term Sheet

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Annex B – Term Facility Term Sheet

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Annex B – Term Facility Term Sheet

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Each such prepayment will be made together with accrued and unpaid interest to the date of prepayment, but without premium or penalty (except breakage costs related to prepayments not made on the last day of the relevant interest period).

Annex B – Term Facility Term Sheet

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Annex B – Term Facility Term Sheet

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Annex B – Term Facility Term Sheet

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Annex B – Term Facility Term Sheet

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Annex B – Term Facility Term Sheet

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Annex B – Term Facility Term Sheet

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Annex B – Term Facility Term Sheet

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Annex B – Term Facility Term Sheet

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Annex B – Term Facility Term Sheet

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SCHEDULE I TO ANNEX B

INTEREST RATES ON THE 364-DAY TERM LOANS

Schedule I to Annex B –Term Facility Term Sheet

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ANNEX C

$400,000,000 364-DAY TERM LOAN FACILITY

CONDITIONS ANNEX

Capitalized terms not otherwise defined herein shall have the meanings assigned to them in the Commitment Letter to which this Annex is attached, or Annex A or Annex B to the Commitment Letter

Subject in all respects to the Limited Conditionality Provision, the availability and the making of the extensions of credit under the Facilities will be subject solely to the satisfaction or waiver of the following conditions precedent:

1.    Subject to the Limited Conditionality Provision, the execution and delivery by the Borrower of the Term Loan Documentation (the “Financing Documentation”), which shall be consistent, in each case, with the Commitment Documents and the Term Loan Documentation Principles.

2.    Subject to the Limited Conditionality Provision, the Administrative Agent and the Lead Arrangers shall have received customary legal opinions, evidence of authorization, organizational documents, good standing certificates (with respect to the jurisdiction of incorporation of the Borrower), a customary closing certificate, a customary officer’s certificate and documents and instruments necessary to establish that the Administrative Agent will have perfected security interests in the Collateral.

3.    The Acquisition shall be consummated prior to or substantially concurrently with the initial funding of the Term Facility in all material respects on the terms set forth in the Acquisition Agreement without giving effect to any modifications thereunder, or any waiver or consent thereunder by the Borrower or at the Borrower’s request, in each case, that is materially adverse to the interests of the Lenders, it being understood that (a) any reduction in the purchase price set forth in the Acquisition Agreement shall not be deemed to be materially adverse to the interests of the Lenders so long as any such reduction is applied to reduce the amount of commitments in respect of the Term Facility on a dollar-for-dollar basis, (b) any increase in the purchase price set forth in the Acquisition Agreement shall not be deemed to be materially adverse to the interests of the Lenders so long as the purchase price increase is not funded with additional indebtedness, (c) any modification, amendment, consent, waiver or determination in respect of the definition of “Company Material Adverse Effect” (as defined in the Acquisition Agreement) shall be deemed to be materially adverse to the interests of the Lenders unless approved by the Lead Arrangers and (d) any change in any of the provisions relating to the Lead Arrangers’ or the Lenders’ liability, consent rights over certain amendments or waivers or status as a third party beneficiary under the Acquisition Agreement, shall be deemed to be materially adverse to the interests of the Lenders unless approved by the Lead Arrangers.

4.    The Lead Arrangers shall have received (a) audited consolidated balance sheets and related statements of income, changes in stockholders equity and cash flows of each of the Borrower and of the Target for the three fiscal years ended at least 90 days prior to the Closing Date and (b) unaudited consolidated balance sheets and related statements of income, changes in equity and cash flows of each of the Borrower and of the Target for each subsequent fiscal quarter following the last fiscal year for which financial statements have been delivered pursuant to clause (a) above ended at least 45 days

Annex C – Conditions Annex

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before the Closing Date. The Lead Arrangers hereby acknowledge receipt of the audited financial statements as at and for the years ended December 31, 2014, 2015 and 2016 for each of the Borrower and the Target and the unaudited financial statements as at and for the quarters ended March 31, 2017, June 30, 2017 and September 30, 2017 for each of the Borrower and the Target.

5.    The Lead Arrangers shall have received a pro forma consolidated balance sheet and the related consolidated statement of income of the Borrower as of and for the twelve-month period ending on the date of the most recent consolidated balance sheet delivered pursuant to the preceding paragraph, in each case prepared after giving effect to the Transactions as if the Transactions had occurred on such date (in the case of such pro forma balance sheet) or on the first day of such period (in the case of such pro forma statement of income).

6.    The Lead Arrangers shall have received a solvency certificate from the chief financial officer of the Borrower in the form attached as Annex D hereto.

7.    The Guarantees with respect to the Term Facility shall have been executed and delivered by the Guarantors and be in full force and effect or substantially simultaneously with the borrowings under the Term Facility, shall be executed and become in full force and effect and (b) all documents and instruments required to perfect the Administrative Agent’s security interest in the Collateral with respect to the Term Facility shall have been executed and delivered by the Borrower and the Guarantors or substantially simultaneously with the borrowings under the Term Facility, shall be executed and delivered by the Borrower and the Guarantors and, if applicable, be in proper form for filing, and none of the Collateral shall be subject to any other pledges, security interest or mortgages, except for the liens permitted under the Term Loan Documentation, liens permitted under the Acquisition Agreement or to be released on or prior to the Closing Date.

8.    The Lead Arrangers shall have received, at least three (3) business days prior to the Closing Date, all documentation and other information regarding the Borrower required by regulatory authorities under applicable “know your customer” and anti-money laundering rules and regulations, including the PATRIOT Act, to the extent requested at least ten (10) business days prior to the Closing Date.

9.    To the extent invoiced at least two (2) business days prior to the Closing Date, all fees and expenses due to the Lead Arrangers, the Administrative Agent and the Lenders required to be paid on the Closing Date (including the fees and expenses of counsel for the Lead Arrangers and the Administrative Agent) will have been paid.

10.    The Borrower shall have engaged (on or before its execution of the Commitment Letter) for any Refinancing and/or Securities Issuance one or more investment and/or commercial banks satisfactory to the Lead Arrangers on terms and conditions satisfactory to the Lead Arrangers for the Refinancing and/or Securities Issuance and/or any other equity or debt issuance the proceeds of which are used to refinance or replace the Term Facility.

11.    The Specified Representations and the Specified Acquisition Agreement Representations will be true and correct in all material respects (or if already qualified by materiality or “material adverse effect”, in all respects).

12.    Since the date of the Acquisition Agreement, there shall not have occurred (and be continuing) a “Company Material Adverse Effect” (as defined in the Acquisition Agreement).

Annex C – Conditions Annex

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ANNEX D

FORM OF SOLVENCY CERTIFICATE

[DATE]

This Solvency Certificate is being executed and delivered pursuant to Section [●] of that certain [●] (the “Credit Agreement”; the terms defined therein being used herein as therein defined).

I, [●], the Chief Financial Officer of Borrower, in such capacity and not in an individual capacity, hereby certify as follows:

IN WITNESS WHEREOF, I have executed this Solvency Certificate on the date first written above.

Annex D – Form of Solvency Certificate

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