WARRANT TO PURCHASE STOCK

Exhibit 4.2(A)

WARRANT TO PURCHASE STOCK

THIS WARRANT AND THE SHARES ISSUABLE HEREUNDER HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE “ACT”), OR THE SECURITIES LAWS OF ANY STATE AND, EXCEPT AND PURSUANT TO THE PROVISIONS OF ARTICLE 5 BELOW, MAY NOT BE OFFERED, SOLD OR OTHERWISE TRANSFERRED, PLEDGED OR HYPOTHECATED UNLESS AND UNTIL REGISTERED UNDER SAID ACT AND APPLICABLE STATE SECURITIES LAW OR, IN THE OPINION OF LEGAL COUNSEL IN FORM AND SUBSTANCE SATISFACTORY TO THE ISSUER OF THESE SECURITIES, SUCH OFFER, SALE OR TRANSFER, PLEDGE OR HYPOTHECATION IS EXEMPT FROM REGISTRATION.

WARRANT TO PURCHASE STOCK

THIS WARRANT CERTIFIES THAT, for the agreed upon value of $1.00 and for other good and valuable consideration, SILICON VALLEY BANK (Silicon Valley Bank, together with any registered holder from time to time of this Warrant or any holder of the shares issuable or issued upon exercise of this Warrant, “Holder”) is entitled to purchase that number of fully paid and nonassessable shares of Series A Preferred set forth above or that number of shares otherwise purchasable upon exercise of this Warrant pursuant to the provisions herein (the “Shares”) at the Warrant Price, as adjusted pursuant to Article 2 of this Warrant and subject to the provisions and upon the terms and conditions set forth in this Warrant. Capitalized terms used but not otherwise defined herein shall have the meanings given them in that certain Loan and Security Agreement in the original principal amount of $2,000,000 dated as of even date herewith by and between the Company and Silicon Valley Bank (the “Loan Agreement”).

ARTICLE 1. EXERCISE.

1.1 Method of Exercise. Holder may exercise this Warrant by delivering a duly executed Notice of Exercise in substantially the form attached as Appendix 1 (the “Notice of Exercise”) to the principal office of the Company. Unless Holder is exercising the conversion right set forth in Section 1.2, Holder shall also deliver to the Company a check, wire transfer (to an account designated by the Company), or other form of payment acceptable to the Company for the aggregate Warrant Price for the Shares being purchased.

1.2 Conversion Right. In lieu of exercising this Warrant as specified in Section 1.1, Holder may from time to time convert this Warrant, in whole or in part, into a number of Shares determined by dividing (a) the aggregate fair market value of the Shares or

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other securities otherwise issuable upon exercise of this Warrant minus the aggregate Warrant Price of such Shares by (b) the fair market value of one Share. The fair market value of the Shares shall be determined pursuant to Section 1.3.

1.3 Fair Market Value. If the Company’s common stock is traded in a public market and the Shares are common stock, the fair market value of each Share shall be the closing price of a Share reported for the business day immediately before Holder delivers its Notice of Exercise to the Company (or in the instance where the Warrant is exercised immediately prior to the effectiveness of the Company’s initial public offering, the “price to public” per share price specified in the final prospectus relating to such offering). If the Company’s common stock is traded in a public market and the Shares are preferred stock, the fair market value of a Share shall be the closing price of a share of the Company’s common stock reported for the business day immediately before Holder delivers its Notice of Exercise to the Company (or, in the instance where the Warrant is exercised immediately prior to the effectiveness of the Company’s initial public offering, the “price to public” per share price specified in the final prospectus relating to such offering), in both cases, adjusted to take into account the number of shares of the Company’s common stock into which a Share is then convertible. If the Company’s common stock is not traded in a public market, the Board of Directors of the Company shall determine fair market value in its reasonable good faith judgment.

1.4 Delivery of Certificate and New Warrant. Promptly after Holder exercises or converts this Warrant and, if applicable, the Company receives payment of the aggregate Warrant Price, the Company shall deliver to Holder certificates for the Shares acquired and, if this Warrant has not been fully exercised or converted and has not expired, a new Warrant representing the Shares not so acquired after taking into account any cashless exercise of this Warrant for Shares purchased in accordance with Section 1.2.

1.5 Replacement of Warrants. On receipt of evidence reasonably satisfactory to the Company of the loss, theft, destruction or mutilation of this Warrant and, in the case of loss, theft or destruction, on delivery of an indemnity agreement reasonably satisfactory in form and amount to the Company or, in the case of mutilation, surrender and cancellation of this Warrant, the Company shall execute and deliver, in lieu of this Warrant, a new warrant of like tenor.

1.6 Treatment of Warrant Upon Acquisition of Company.

(a) “Acquisition”. For the purpose of this Warrant, “Acquisition” means any sale, license, or other disposition of all or substantially all of the assets of the Company, or any reorganization, consolidation, merger or other business combination of the Company with and/or into a third party where the holders of the Company’s securities before the transaction beneficially own less than 50% of the outstanding voting securities of the surviving entity after the transaction.

(b) Treatment of Warrant at Acquisition.

(i) Upon the written request of the Company, Holder agrees that, in the event of an Acquisition in which the sole consideration is cash, either (A) Holder shall

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exercise its conversion or purchase right under this Warrant and such exercise will be deemed effective immediately prior to the consummation of such Acquisition or (B) if Holder elects not to exercise the Warrant, this Warrant will expire upon the consummation of such Acquisition. The Company shall provide the Holder with written notice of its request relating to the foregoing (together with such reasonable information as the Holder may request in connection with such contemplated Acquisition giving rise to such notice), which is to be delivered to Holder not less than ten (10) days prior to the closing of the proposed Acquisition.

(ii) Upon the written request of the Company, Holder agrees that, in the event of an Acquisition that is an “arm’s-length” sale of all or substantially all of the Company’s assets (and only its assets) to a third party that is not an Affiliate, (as defined below) of the Company (a “True Asset Sale”), either (A) Holder shall exercise its conversion or purchase right under this Warrant and such exercise will be deemed effective immediately prior to the consummation of such Acquisition or (B) if Holder elects not to exercise the Warrant, this Warrant will continue until the Expiration Date if the Company continues as a going concern following the closing of any such True Asset Sale. The Company shall provide the Holder with written notice of its request relating to the foregoing (together with such reasonable information as the Holder may request in connection with such contemplated Acquisition giving rise to such notice), which is to be delivered to Holder not less than ten (10) days prior to the closing of the proposed Acquisition.

(iii) Upon the written request of the Company, Holder agrees that, in the event of an Acquisition of the Company by a publicly-traded acquirer in which the consideration to be paid by such acquirer (A) is either (x) shares of stock which are traded on the New York Stock Exchange, NASDAQ National or SmallCap Market or other public securities market in which securities of companies are regularly traded in the United States (“Public Stock”) or (y) a combination of cash and shares of Public Stock and (B) has, on the record date for the Acquisition, a fair market value per share of the Shares (or other securities issuable upon exercise of this Warrant) that is equal to or greater than five times the Warrant Price, the Company may require this Warrant to be deemed automatically exercised, in which case Holder shall participate in the Acquisition as a holder of the Shares (or other securities issuable upon exercise of this Warrant) on the same terms as other holders of the same class and series of securities of the Company. The Company shall provide Holder with written notice of its request relating to the foregoing (together with such reasonable information as Holder may request in connection with the contemplated Acquisition giving rise to such notice), which is to be delivered to Holder not less than ten (10) days prior to the closing of the proposed Acquisition.

(iv) Upon the closing of any Acquisition other than those particularly described in subsections (i), (ii) and (iii) above, the successor entity shall assume the obligations of this Warrant, and this Warrant shall be exercisable for the same securities, cash, and property as would be payable for the Shares issuable upon exercise of the unexercised portion of this Warrant as if such Shares were outstanding on the record date for the Acquisition and its subsequent closing. In such instance, the Warrant Price and/or number of Shares shall be adjusted accordingly such that the aggregate Warrant Price payable by Holder upon the exercise of the unexercised portion of this Warrant shall remain unchanged.

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As used herein “Affiliate” shall mean any person or entity that owns or controls directly or indirectly ten (10) percent or more of the stock of Company, any person or entity that controls or is controlled by or is under common control with such persons or entities, and each of such person’s or entity’s officers, directors, joint venturers or partners, as applicable.

ARTICLE 2. ADJUSTMENTS TO THE SHARES.

2.1 Stock Dividends, Splits, Etc. If the Company declares or pays a dividend on the shares of Series A Preferred payable in common stock, or other securities, then upon exercise of this Warrant, for each Share acquired, Holder shall receive, without cost to Holder, the total number and kind of securities to which Holder would have been entitled had Holder owned the Shares of record as of the date the dividend occurred. If the Company subdivides the shares of Series A Preferred by reclassification or otherwise into a greater number of shares or takes any other action which increase the amount of securities into which the shares of Series A Preferred are convertible, the number of Shares purchasable hereunder shall be proportionately increased and the Warrant Price shall be proportionately decreased. If the outstanding shares of Series A Preferred are combined or consolidated, by reclassification or otherwise, into a lesser number of shares, the Warrant Price shall be proportionately increased and the number of Shares shall be proportionately decreased.

2.2 Reclassification, Exchange, Combinations or Substitution. Upon any reclassification, exchange, substitution, or other event not constituting an Acquisition that results in a change of the number and/or class of the securities issuable upon exercise or conversion of this Warrant, Holder shall be entitled to receive, upon exercise or conversion of this Warrant, the number and kind of securities and property that Holder would have received for the Shares if this Warrant had been exercised immediately before such reclassification, exchange, substitution, or other event. Such an event shall include any automatic conversion of the outstanding or issuable securities of the Company of the same class or series as the Shares to common stock pursuant to the terms of the Company’s Amended and Restated Certificate of Incorporation in effect upon the Issue Date (the “Restated Certificate”) and any amendment of the Restated Certificate by the Company’s stockholders from time to time hereafter, or, if applicable, upon the closing of a registered public offering of the Company’s common stock. The Company or its successor shall promptly issue to Holder an amendment to this Warrant setting forth the number and kind of such new securities or other property issuable upon exercise or conversion of this Warrant as a result of such reclassification, exchange, substitution or other event that results in a change of the number and/or class of securities issuable upon exercise or conversion of this Warrant. The amendment to this Warrant shall provide for adjustments which shall be as nearly equivalent as may be practicable to the adjustments provided for in this Article 2 including, without limitation, adjustments to the Warrant Price and to the number of securities or property issuable upon exercise of the new Warrant. The provisions of this Section 2.2 shall similarly apply to successive reclassifications, exchanges, substitutions, or other events.

2.3 Adjustments for Diluting Issuances. The Warrant Price and the number of Shares issuable upon exercise of this Warrant or, if the Shares are preferred stock, the number of shares of common stock issuable upon conversion of the Shares shall be subject to adjustment, from time to time in the manner set forth in the Restated Certificate as if the Shares were issued and outstanding on and as of the date of any such required adjustment. The provisions set forth

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for the Shares in the Restated Certificate relating to the above may not be amended, modified or waived, without the prior written consent of Holder unless such amendment, modification or waiver affects the rights granted to Holder associated with the Shares in the same manner as such amendment, modification or waiver affects the rights associated with all other shares of the same series and class as the Shares.

2.4 Adjustment for Termination of Loan Obligation. In the event that Silicon Valley Bank terminates its obligation to lend to the Company the undisbursed portion of the Committed Equipment Line pursuant to Section 2.2 of the Loan Agreement, the number of Shares issuable upon exercise of this Warrant shall be equal to the product of (i) the number of Shares issuable upon exercise of this Warrant at such time, multiplied by (ii) the quotient of (x) the aggregate of all Equipment Advances made under the Loan Agreement prior to such time, divided by (y) the total Committed Equipment Line (i.e., $2,000,000).

2.5 No Impairment. Subject to the circumstances described in Sections 1.6, 2.2 and 2.3 which affect this Warrant, the Company shall not, by amendment of its Restated Certificate or through a reorganization, transfer of assets, consolidation, merger, dissolution, issue, or sale of securities or any other voluntary action, avoid or seek to avoid the observance or performance of any of the terms to be observed or performed under this Warrant by the Company, but shall at all times in good faith assist in carrying out of all the provisions of this Article 2 and in taking all such action as may be necessary or appropriate to protect Holder’s rights under this Article 2 against impairment.

2.5 Fractional Shares. No fractional Shares shall be issuable upon exercise or conversion of the Warrant and the number of Shares to be issued shall be rounded down to the nearest whole Share. If a fractional share interest arises upon any exercise or conversion of the Warrant, the Company shall eliminate such fractional share interest by paying Holder the amount computed by multiplying the fractional interest by the fair market value of a full Share.

2.6 Certificate as to Adjustments. Upon each adjustment of the Warrant Price, the Company shall promptly notify Holder in writing, and, at the Company’s expense, promptly compute such adjustment, and furnish Holder with a certificate of its Chief Financial Officer or other Responsible Officer setting forth such adjustment and the facts upon which such adjustment is based. The Company shall, upon written request, furnish Holder a certificate setting forth the Warrant Price in effect upon the date thereof and the series of adjustments leading to such Warrant Price.

ARTICLE 3. REPRESENTATIONS AND COVENANTS OF THE COMPANY.

3.1 Representations and Warranties. The Company represents and warrants to Holder as follows:

(a) As of the Issue Date, the initial Warrant Price referenced on the first page of this Warrant (i) is the price per share of the Series A Preferred at which such shares were last issued in an arms-length transaction in which at least $500,000 of the Series A Preferred were sold and (ii) is not greater than the fair market value of a share of the Series A Preferred as of the date of this Warrant.

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(b) All Shares which may be issued upon the exercise of the purchase right represented by this Warrant, and all securities, if any, issuable upon conversion of the Shares, shall, upon issuance, be duly authorized, validly issued, fully paid and nonassessable, and free of any liens and encumbrances except for restrictions on transfer provided for herein, under applicable federal and state securities laws, or under the Company’s bylaws.

(c) The capitalization table attached hereto as Exhibit A completely and accurately reflects the Company’s capitalization as of the Issue Date.

3.2 Notice of Certain Events. If the Company proposes at any time (a) to declare any dividend or distribution upon any of its stock, whether in cash, property, stock, or other securities and whether or not a regular cash dividend; (b) to effect any reclassification or recapitalization of any of its stock; (c) to merge or consolidate with or into any other corporation, or sell, lease, license, or convey all or substantially all of its assets, or to liquidate, dissolve or wind up; or (d) offer holders of Series A Preferred the opportunity to participate in an underwritten public offering of the Company’s securities for cash, then, in connection with each such event, the Company shall give Holder: (1) at least 10 days prior written notice of the date on which a record will be taken for such dividend, distribution, or subscription rights (and specifying the date on which the holders of common stock will be entitled thereto) or for determining rights to vote, if any, in respect of the matters referred to in (a); (2) in the case of the matters referred to in (b) and (c) above at least 10 days prior written notice of the date when the same will take place (and specifying the date on which the holders of common stock will be entitled to exchange their common stock for securities or other property deliverable upon the occurrence of such event); and (3) in the case of the matter referred to in (d) above, the same notice as is given to the holders of such Series A Preferred.

3.3 Registration Under Securities Act of 1933, as amended (the “Act”). The Company agrees that the Shares or, if the Shares are convertible into common stock of the Company, such common stock, shall have certain incidental, or “piggyback,” and Form S-3 registration rights pursuant to and as set forth in the Investor Rights Agreement dated as of August 19, 2004, as amended by the Amendment of even date herewith between the Company and Holder (the “Rights Agreement”). The provisions set forth in the Rights Agreement relating to the above in effect as of the Issue Date may not be amended, modified or waived without the prior written consent of Holder unless such amendment, modification or waiver affects all holders of Series A Preferred in the same manner.

3.4 No Stockholder Rights. Except as provided in this Warrant, Holder will not have any rights as a stockholder of the Company until the exercise of this Warrant. Notwithstanding anything to the contrary contained herein, the Company acknowledges and agrees that the Shares shall not be subject to the provisions of Section B.4 of Article Fourth of the Restated Certificate, and the Company shall take, or cause to be taken, all actions reasonably necessary or advisable from time to time with respect thereto.

ARTICLE 4. REPRESENTATIONS, WARRANTIES OF HOLDER. Holder represents, warrants, and covenants to the Company as follows:

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4.1 Purchase for Own Account. This Warrant and the securities to be acquired upon exercise of this Warrant (or upon conversion thereof) by Holder (collectively, the “Securities”) will be acquired for investment for Holder’s account, not as a nominee or agent, and not with a view to the public resale or distribution within the meaning of the Act. Holder also represents that Holder has not been formed for the specific purpose of acquiring the Securities.

4.2 Disclosure of Information. Holder has received or has had full access to all the information it considers necessary or appropriate to make an informed investment decision with respect to the acquisition of this Warrant and the Securities. Holder further has had an opportunity to ask questions and receive answers from the Company regarding the terms and conditions of the offering of this Warrant and the Securities and to obtain additional information (to the extent the Company possessed such information or could acquire it without unreasonable effort or expense) necessary to verify any information furnished to Holder or to which Holder has access.

4.3 Investment Experience. Holder understands that the purchase of this Warrant and the Securities involves substantial risk. Holder has experience as an investor in securities of companies in the development stage and acknowledges that Holder can bear the economic risk of such Holder’s investment in this Warrant and the Securities and has such knowledge and experience in financial or business matters that Holder is capable of evaluating the merits and risks of its investment in this Warrant and the Securities and/or has a preexisting personal or business relationship with the Company and certain of its officers, directors or controlling persons of a nature and duration that enables Holder to be aware of the character, business acumen and financial circumstances of such persons.

4.4 Accredited Investor Status. Holder is an “accredited, investor” within the meaning of Regulation D promulgated under the Act.

4.5 The Act. Holder understands that this Warrant and the Shares issuable upon exercise or conversion hereof have not been registered under the Act in reliance upon a specific exemption therefrom, which exemption depends upon, among other things, the bona fide nature of Holder’s investment intent as expressed herein. Holder understands that this Warrant and the Shares issued upon any exercise or conversion hereof must be held indefinitely unless subsequently registered under the Act and qualified under applicable state securities laws, or unless exemption from such registration and qualification are otherwise available.

4.6 Standoff Agreement. With respect to the Company’s initial public offering, upon request of the Company or the underwriters managing such offering, Holder hereby agrees that Holder shall not sell or otherwise transfer or dispose of any Shares (or other securities) of the Company held by Holder during a reasonable and customary period of time as agreed to by the Company and the underwriters, not to exceed one hundred eighty (180) days following the effective date of the registration statement of the Company filed under the Act with respect of such offering, provided that:

(a) all officers and directors of the Company and all other holders of at least one percent (1%) or more of the Company’s securities enter into similar agreements; and

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(b) any discretionary waiver or termination of the restrictions of any similar agreement by the Company or representatives of the underwriters shall apply to Holder on a pro rata basis together with all other holders of securities with respect to which such agreement was waived or terminated.

Holder agrees to execute and deliver such other agreements as may be reasonably requested by the Company or the underwriter which are consistent with the foregoing or which are necessary to give further effect hereto. The obligations described in this Section 4.6 shall not apply to any registration relating solely to employee benefit plans on Form S-1 or Form S-8 or similar forms that may be promulgated in the future, or any registration relating solely to a transaction covered by Rule 145 under the Act on Form S-4 or similar forms that may be promulgated in the future.

ARTICLE 5. MISCELLANEOUS.

5.1 Term: This Warrant is exercisable in whole or in part at any time and from time to time on or before the earlier of (i) October 14, 2011 (provided, however, that, if neither an Acquisition nor an initial public offering of the Company’s securities pursuant to a firm commitment underwriting (an “IPO”) shall have been consummated prior to such date, such date shall be extended automatically to October 14, 2014), or (ii) the second anniversary of the closing of an IPO (the “Expiration Date”).

5.2 Legends. This Warrant and the Shares (and the securities issuable, directly or indirectly, upon conversion of the Shares, if any) shall be imprinted with legends in substantially the following forms (if and to the extent applicable):

THIS WARRANT AND THE SHARES ISSUABLE HEREUNDER HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE “ACT”), OR THE SECURITIES LAWS OF ANY STATE AND, EXCEPT AND PURSUANT TO THE PROVISIONS OF ARTICLE 5 OF THIS WARRANT, MAY NOT BE OFFERED, SOLD OR OTHERWISE TRANSFERRED, PLEDGED OR HYPOTHECATED UNLESS AND UNTIL REGISTERED UNDER THE ACT AND APPLICABLE STATE SECURITIES LAW OR, IN THE OPINION OF LEGAL COUNSEL IN FORM AND SUBSTANCE SATISFACTORY TO THE ISSUER OF THESE SECURITIES, SUCH OFFER, SALE OR TRANSFER, PLEDGE OR HYPOTHECATION IS EXEMPT FROM REGISTRATION.

A STATEMENT OF THE RIGHTS, PREFERENCES, PRIVILEGES AND RESTRICTIONS GRANTED TO OR IMPOSED ON EACH CLASS OR SERIES OF CAPITAL STOCK AUTHORIZED TO BE ISSUED AND ON THE HOLDERS THEREOF WILL BE FURNISHED WITHOUT CHARGE TO ANY STOCKHOLDER UPON WRITTEN REQUEST TO THE CORPORATION.

THE SHARES REPRESENTED BY THIS CERTIFICATE ARE SUBJECT TO A DAY MARKET STANDOFF RESTRICTION AS SET FORTH IN A CERTAIN AGREEMENT BETWEEN THE ISSUER AND THE ORIGINAL HOLDER OF THESE SHARES, A COPY OF WHICH MAY BE OBTAINED

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AT THE PRINCIPAL OFFICE OF THE ISSUER. SUCH RESTRICTION IS BINDING ON TRANSFEREES OF THESE SHARES.

5.3 Compliance with Securities Laws on Transfer. This Warrant and the Shares issuable upon exercise of this Warrant (and the securities issuable, directly or indirectly, upon conversion of the Shares, if any) may not be transferred or assigned in whole or in part without compliance with applicable federal and state securities laws by the transferor and the transferee (including, without limitation, the delivery of investment representation letters and legal opinions reasonably satisfactory to the Company, as reasonably requested by the Company). The Company shall not require Holder to provide an opinion of counsel if the transfer is to Silicon Valley Bancshares (Holder’s parent company) or any other Affiliate of Holder. Additionally, the Company shall also not require an opinion of counsel if there is no material question as to the availability of current information as referenced in Rule 144(c) under the Act, Holder represents that it has complied with Rule 144(d) under the Act and Rule 144(e) under the Act in reasonable detail, the selling broker represents that it has complied with Rule 144(f) under the Act, and the Company is provided with a copy of Holder’s notice of proposed sale.

5.4 Transfer Procedure. Upon receipt by Holder of the executed Warrant, Holder will transfer all of this Warrant to Silicon Valley Bancshares, Holder’s parent company, by execution of an Assignment substantially in the form of Appendix 2. Subject to the provisions of Section 5.3 and upon providing Company with written notice, Silicon Valley Bancshares and any subsequent Holder may transfer all or part of this Warrant or the Shares issuable upon exercise of this Warrant (or the securities issuable directly or indirectly, upon conversion of the Shares, if any) to any transferee, provided, however, in connection with any such transfer, Silicon Valley Bancshares or any subsequent Holder will give the Company notice of the portion of the Warrant being transferred with the name, address and taxpayer identification number of the transferee and Holder will surrender this Warrant to the Company for reissuance to the transferee(s) (and Holder if applicable). The Company may refuse to transfer this Warrant or the Shares to any person who directly competes with the Company, unless, in either case, the stock of the Company is publicly traded. The Company may also refuse to transfer some or all of this Warrant or the Shares to more than 10 different transferees of Holder.

5.5 Notices. All notices and other communications from the Company to Holder, or vice versa, shall be deemed delivered and effective when given personally or mailed by first-class registered or certified mail, postage prepaid (or on the first business day after transmission by facsimile), at such address as may have been furnished to the Company or Holder, as the case may be, in writing by the Company or such holder from time to time. Effective upon receipt of the fully executed Warrant and the initial transfer described in Section 5.4 above, all notices to Holder shall be addressed as follows until the Company receives notice of a change of address in connection with a transfer or otherwise:

Silicon Valley Bancshares

Attn: Treasury Department

3003 Tasman Drive, HA 200

Santa Clara, CA 95054

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Telephone: 408 ###-###-####

Facsimile: 408 ###-###-####

Notice to the Company shall be addressed as follows until Holder receives notice of a change in address:

OncoMed Pharmaceuticals, Inc.

Attn: CEO

265 N. Whisman Road

Mountain View, CA 94043

Telephone: (415)  ###-###-####

Facsimile: (415)  ###-###-####

5.6 Waiver. This Warrant and any term hereof may be changed, waived, discharged or terminated only by an instrument in writing signed by the party against which enforcement of such change, waiver, discharge or termination is sought.

5.7 Attorneys’ Fees. In the event of any dispute between the parties concerning the terms and provisions of this Warrant, the party prevailing in such dispute shall be entitled to collect from the other party all costs incurred in such dispute, including reasonable attorneys’ fees.

5.8 Automatic Conversion upon Expiration. In the event that, upon the Expiration Date, the fair market value of one Share (or other security issuable upon the exercise hereof) as determined in accordance with Section 1.3 above is greater than the Exercise Price in effect on such date, then this Warrant shall automatically be deemed on and as of such date to be converted pursuant to Section 1.2 above as to all Shares (or such other securities) for which it shall not previously have been exercised or converted, and the Company shall promptly deliver a certificate representing the Shares (or such other securities) issued upon such conversion to Holder.

5.9 Counterparts. This Warrant may be executed in counterparts, all of which together shall constitute one and the same agreement.

5.10 Governing Law. This Warrant shall be governed by and construed in accordance with the laws of the State of California, without giving effect to its principles regarding conflicts of law.

IN WITNESS WHEREOF, the Company has caused this Warrant to be duly executed and delivered as of the Issue Date specified above.

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EXHIBIT A

Capitalization Table

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APPENDIX 1

NOTICE OF EXERCISE

1. Holder elects to purchase                                          shares of the Common/Series A Preferred [strike one] Stock of OncoMed Pharmaceuticals, Inc. (the Company”) pursuant to the terms of the attached Warrant, and tenders payment of the purchase price of the shares in full.

[or]

1. Holder elects to convert the attached Warrant into Shares/cash [strike one] in the manner specified in the Warrant. This conversion is exercised for                                          of the Shares covered by the Warrant.

[Strike paragraph that does not apply.]

2. Please issue a certificate or certificates representing the shares in the name specified below:

3. By its execution below and for the benefit of the Company, Holder hereby restates each of the representations and warranties in Article 4 of the Warrant as the date hereof.

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APPENDIX 2

ASSIGNMENT

For value received, Silicon Valley Bank hereby sells, assigns and transfers unto:

that certain Warrant to Purchase Stock issued by OncoMed Pharmaceuticals, Inc. (the “Company”), on October 14, 2004 (the “Warrant”), together with all rights, title and interest therein.

By its execution below, and for the benefit of the Company, Silicon Valley Bancshares makes each of the representations and warranties set forth in Article 4 of the Warrant as of the date hereof and acknowledges and agrees to be bound by the terms of the Warrant.

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