WARRANT TO PURCHASE STOCK

Exhibit 10.29

THIS WARRANT AND THE SHARES ISSUABLE HEREUNDER HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED, AND MAY NOT BE SOLD, PLEDGED OR OTHERWISE TRANSFERRED OTHER THAN IN ACCORDANCE WITH APPLICABLE LAW.

WARRANT TO PURCHASE STOCK

THIS WARRANT CERTIFIES THAT, for good and valuable consideration, the receipt of which is hereby acknowledged, COMERICA BANK - CALIFORNIA or its assignee (“Holder”) is entitled to purchase the number of folly paid and nonassessable shares of the class of securities (the “Shares”) of the corporation (the “Company”) at the initial exercise price per Share (the “Warrant Price”) all as set forth above and as adjusted pursuant to Article 2 of this warrant, subject to the provisions and upon the terms and conditions set forth in this warrant. The Shares shall have the rights, restrictions and privileges set forth in the Certificate of Incorporation of the Company, as amended or restated from time to time (the “Certificate of Incorporation”). If all of the outstanding Shares are converted into Common Stock of the Company in accordance with the terms of the Certificate of Incorporation of the Company, then, effective upon such conversion, (i) this Warrant shall be exercisable for such number of Shares of Common Stock as is equal to the number of shares of Common Stock that each Share was converted into, multiplied by the number of Shares subject to this Warrant immediately prior to such conversion, (ii) the Warrant Price shall be the Warrant Price in effect immediately prior to such conversion divided by the number of shares of Common Stock into which each Share was converted, and (iii) all references in this Warrant to “Series A Preferred Stock” or Shares” shall thereafter be deemed to refer to “Common Stock.”

ARTICLE 1. EXERCISE.

1.1 Method of Exercise. Holder may exercise this warrant by delivering this warrant and a duly executed Notice of Exercise in substantially the form attached as Appendix 1 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 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 other securities otherwise issuable upon exercise of this warrant (calculated by multiplying the fair market value of one Share at the time of exercise by the aggregate number of Shares then underlying the 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 Shares are traded regularly on a national securities exchange, the Nasdaq National Market or other nationally recognized trading system, the fair market value of the Shares shall be the average closing price of the Shares (or the closing price of the Company’s stock into which the Shares are convertible) reported for the five (5) business days immediately before the date on the Notice of Exercise delivered by the Holder to the Company. If the Shares are not regularly traded on a national securities exchange, the Nasdaq National Market or other nationally recognized trading system, 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, 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.

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, on surrender and cancellation of this warrant, the Company at its expense shall execute and deliver, in lieu of this warrant, a new warrant of like tenor.

ARTICLE 2. ADJUSTMENTS TO THE SHARES.

2.1 Stock Dividends, Splits, Etc.

(a) Stock Splits and Combinations of Preferred Stock. If outstanding shares of the Company’s Series A Preferred Stock shall be subdivided into a greater number of shares or a dividend shall be paid in respect of the Series A Preferred Stock other than accruing dividends payable pursuant to the Certificate of Incorporation, the Warrant Price in effect immediately prior to such subdivision or at the record date of such dividend shall simultaneously with the effectiveness of such subdivision or immediately after the record date of such dividend be proportionately reduced. If outstanding shares of Series A Preferred Stock shall be combined into a smaller number of shares, the Warrant Price with respect to such shares of Series A Preferred Stock in effect immediately prior to such combination shall, simultaneously with the effectiveness of such combination, be proportionately increased. When any adjustment is required to be made in the Warrant Price in accordance with this Section 2.1(a), the number of Shares purchasable upon the exercise of this Warrant shall be changed to the number determined by dividing (i) an amount equal to the number of shares issuable upon the exercise of this Warrant immediately prior to such adjustment, multiplied by the Warrant Price in effect immediately prior to such adjustment, by (ii) the Warrant Price in effect immediately after such adjustment.

(b) Stock Splits and Combinations of Common Stock. After any mandatory conversion of shares of Series A Preferred Stock pursuant to the Company’s Certificate of Incorporation, (i) if outstanding shares of the Company’s Common Stock shall be subdivided into a greater number of shares or a dividend in Common Stock shall be paid in respect of Common Stock, the Warrant Price in effect immediately prior to such subdivision or at the record date of such dividend shall simultaneously with the effectiveness of such subdivision or immediately after the record date of such dividend be proportionately reduced and (ii) if outstanding shares of Common Stock shall be combined into a smaller number of shares, the Warrant Price with respect to such shares of Common Stock in effect immediately prior to such combination shall, simultaneously with the effectiveness of such combination, be proportionately increased. When any adjustment in required to be made in the Warrant Price pursuant to this Section 2.1(b), the number of Shares purchasable upon the exercise of this Warrant shall be changed to the number determined by dividing (i) an amount equal to the number of shares issuable upon the exercise of this Warrant immediately prior to such adjustment, multiplied by the Warrant Price in effect immediately prior to such adjustment, by (ii) the Warrant price in effect immediately after such adjustment.

2.2 Reclassification, Exchange or Substitution. Upon any reclassification, exchange, substitution, or other event that results in a change of the number and/or class of the securities issuable upon exercise or conversion of this warrant (other than a change in par value or a change provided for in Section 2.1 above), or any consolidation or merger of the Company with or into another corporation, whether or not the Company is the surviving corporation, lawful provision shall be made so that 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. In any such case, appropriate adjustment (as reasonably determined in good faith by the Board of Directors of the Company) shall be made in the application of the provisions set forth herein with respect to the rights and interests thereafter of the Holder of this Warrant, such that the provisions set forth in this Section 2 (including provisions with respect to adjustment of the Warranty Price) shall thereafter be applicable, as nearly as is reasonably practicable, in relation to any shares of stock or other securities or property thereafter deliverable upon the exercise of this Warrant.

2.3 Adjustments for Diluting Issuances. Additional antidilution rights applicable to the Series A Preferred Stock purchasable hereunder are as set forth in the Certificate of Incorporation.

2

2.4 No Impairment. The Company shall not, by amendment of its Certificate of Incorporation 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 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 against impairment.

2.5 Certificate as to Adjustments. Upon each adjustment of the Warrant Price, the Company at its expense shall promptly compute such adjustment, and furnish Holder with a certificate of its Chief Financial 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.

2.6 Assumption of Warrant. If upon the closing of any Acquisition the successor entity assumes the obligations of this warrant, then 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 subsequent closing. The Warrant Price shall be adjusted accordingly. The Company shall use reasonable efforts to cause the surviving corporation to assume the obligations of this warrant. For the purpose of this warrant, “Acquisition” means any sale, license, or other disposition of all or substantially all of the assets (including intellectual property) of the Company, or any reorganization, consolidation, or merger of the Company 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.

ARTICLE 3. REPRESENTATIONS AND COVENANTS OF THE COMPANY.

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

(a) The initial Warrant Price referenced on the first page of this warrant is not greater than the fair market value of the Shares, as determined in good faith by the Board of Directors, as of the date of this warrant.

(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 in accordance with the terms of the Warrant, be duly authorized, validly issued, fully paid and nonassessable, and free of any liens and encumbrances except for restrictions on transfer provided for herein or under applicable federal and state securities laws.

(c) The Company’s capitalization table attached to this warrant is true and complete 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 its common 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 common stock; or (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, then, in connection with each such event, the Company shall give Holder (1) at least 20 days prior written notice of the date on which a record will be taken for such dividend or distribution (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); and (2) in the case of the matters referred to in (b) and (c) above at least 20 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).

3.3 Information Rights. So long as the Holder holds this warrant and/or any of the Shares, the Company shall deliver to the Holder (a) promptly after mailing, copies of all communiques to the shareholders of the Company, (b) within ninety (90) days after the end of each fiscal year of the Company, the annual audited financial statements of the Company certified by independent public accountants of recognized standing and (c) within forty-five (45) days after the end of each of the first three quarters of each fiscal year, the Company’s quarterly, unaudited financial statements.

3

3.4 Registration Under Securities Act of 1933, as amended. The Company agrees that it shall use its best efforts to amend the Investors Rights Agreement such that, upon exercise of the Warrant, the common stock of the Company into which the Shares are convertible shall be deemed “Registrable Shares”, and Holder shall be entitled to the rights of a “Purchaser.”

3.4 Representations and Warranties of the Holder. The Holder represents and warrants to the Company as follows:

(a) Investment. The Holder is acquiring the Warrant, the Shares, and the shares of common stock into which the Shares may be converted, for its own account for investment and not with a view to, or for sale in connection with, any distribution thereof, nor with any present intention of distributing or selling the same; and the Holder has no present or contemplated agreement, undertaking, arrangement, obligation, indebtedness or commitment providing for the disposition thereof. The Holder acknowledges that an investment in the securities acquirable pursuant to this Warrant is speculative and involves a high degree of risk and that a purchase of such securities should only be made by persons who can afford the entire loss of their investment. The Holder is an “accredited investor” as defined in Rule 501 (a) under the Act. The Holder further understands that this Warrant has 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 the Holder’s investment intent as expressed herein.

(b) Authority. The Holder has full power and authority to enter into and to perform this Agreement in accordance with its terms. Any Holder that is a corporation, partnership or trust represents that it has not been organized, reorganized or recapitalized specifically for the purpose of investing in the Company.

(c) Experience. The Holder has carefully reviewed the representations concerning the Company contained in this Warrant and has made detailed inquiry concerning the Company, its business and its personnel; the officers of the Company have made available to the Holder any and all written information which it has requested and have answered to such Holder’s satisfaction all inquiries made by the Holder, and the Holder has sufficient knowledge and experience in finance and business that it is capable of evaluating the risks and merits of its investment in the Company and the Holder is able financially to bear the risks thereof.

(d) No Impairment. The Company will not, by amendment of its charter or through 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 of this Warrant, but will at all times in good faith assist in the carrying out of all such terms and in the taking of all such action as may be necessary or appropriate in order to protect the rights of the holder of this Warrant against impairment.

ARTICLE 4. MISCELLANEOUS.

4.1 Term. This warrant is exercisable in whole or in part, at any time and from time to time on or before the Expiration Date set forth above.

4.2 Legends. This warrant and the Shares (and the securities issuable, directly or indirectly, upon conversion of the Shares, if any) shall be imprinted with a legend in substantially the following form:

THIS SECURITY HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED, AND MAY NOT BE SOLD, PLEDGED OR OTHERWISE TRANSFERRED EXCEPT IN ACCORDANCE WITH APPLICABLE LAW.

4.3 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.

4

4.4 Transfer Procedure. Subject to the provisions of Section 4.3, 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) by giving the Company notice of the portion of the warrant being transferred setting forth the name, address and taxpayer identification number of the transferee and surrendering this warrant to the Company for reissuance to the transferee(s) (and Holder, if applicable); provided, however, that Holder may transfer all or part of this warrant to its affiliates, including, without limitation, Comerica Incorporated, at any time without notice to the Company, and such affiliate shall then be entitled to all the rights of Holder under this warrant and any related agreements, and the Company shall cooperate fully in ensuring that any stock issued upon exercise of this warrant is issued in the name of the affiliate that exercises the warrant. The terms and conditions of this warrant shall inure to the benefit of, and be binding upon, the Company and the holders hereof and their respective permitted successors and assigns.

4.5 Notices. All notices and other communications from the Company to the Holder, or vice versa, shall be deemed delivered and effective when given personally or mailed by first-class registered or certified mail, postage prepaid, at such address as may have been furnished to the Company or the Holder, as the case may be, in writing by the Company or such Holder from time to time. All notices to the Holder shall be addressed as follows:

Comerica Bank - California

Attn: Warrant Administrator

Technology and Life Sciences Division

P.O. Box 7279

San Francisco, CA 94120-7279

4.6 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.

4.7 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.

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

4.9 Agreement in Connection with Public Offering. The Holder agrees, in connection with the initial underwritten public offering of the Company’s securities pursuant to a registration statement under the Act, (i) not to sell, make short sale of, loan, grant any options for the purchase of, or otherwise dispose of any shares of common stock held by the Holder (other than any shares included in the offering) without the prior written consent of the Company or the underwriters managing such initially underwritten public offering of the Company’s securities for a period of 180 days from the effective date of such registration statement, and (ii) to execute any agreement reflecting clause (i) above as may be requested by the Company or the managing underwriters at the time of such offering; provided that the Holder shall be subject to this Section 4.9 as long as all stockholders of the Company then holding at least 5% of the outstanding common stock (on an as converted basis) and all officers and directors of the Company are subject to similar agreements.

5

APPENDIX 1

NOTICE OF EXERCISE

1. The undersigned hereby elects to purchase                      shares of the                      stock of GenPath Pharmaceuticals, Inc. pursuant to the terms of the attached warrant, and tenders herewith payment of the purchase price of such shares in full.

2. The undersigned hereby elects to convert the attached warrant into shares in the manner specified in the warrant. This conversion is exercised with respect to                      of the shares covered by the warrant.

[Strike paragraph that does not apply.]

3. Please issue a certificate or certificates representing said shares in the name of the undersigned or in such other name as is specified below:

Comerica Bank - California

Arm: Warrant Administrator

Technology and Life Sciences Division

P.O. Box 7279

San Francisco, CA 94120-7279

OR Registered Assignee

4. The undersigned represents it is acquiring the shares solely for its own account and not as a nominee for any other party and not with a view toward the resale or distribution thereof except in compliance with applicable securities laws.

6