CANCER PREVENTION PHARMACEUTICALS,INC. AMENDMENT TO Rightof First Refusal and Co-Sale Agreement

Exhibit 10.17

CANCER PREVENTION PHARMACEUTICALS, INC.

AMENDMENT TO Right of First Refusal and Co-Sale Agreement

This Amendment to Right of First Refusal and Co-Sale Agreement (“Amendment”) is made as of September 27, 2012 by and between Cancer Prevention Pharmaceuticals, Inc., a Delaware corporation (the “Company”) and the undersigned Investors and Founders. Capitalized terms used but not otherwise defined herein shall have the meanings assigned to such terms in that certain Right of First Refusal and Co-Sale Agreement dated as of September 17, 2012 between the Company and the Investors and Founders (the “Agreement”).

WHEREAS, together, the undersigned Investors and Founders and the Company are authorized and desire to amend the Agreement in the manner herein provided.

NOW THEREFORE, in consideration of the mutual covenants, promises and agreements of the Company and the undersigned Investors and other good and valuable consideration, the receipt and sufficiency of which are hereby acknowledged, the parties hereby agree as follows:

B.          Certain holders (“Note Holders”) of the Company’s Convertible Promissory Notes (“Notes”) are desirous of converting, or have converted, the principal amount of and accrued interest on the Notes into the Company’s Series A-1 Convertible Preferred Stock (“Series A-1 Preferred”) in accordance with the terms of the Series A-1 Preferred Stock Purchase Agreement (the “Conversion”).

C.          The Company proposes to sell (“Financing”) shares of its Series A-2 Convertible Preferred Stock (“Series A-2 Preferred”) to the purchasers identified on Series A-2 Preferred Stock Purchase Agreement (the “Purchase Agreement”).

D.          The Investors are, or will be, either (i) former Note Holders which have been converted pursuant to the Conversion or (ii) purchasers of Series A-2 Preferred listed in the Purchase Agreement.

E.         As a condition to the Financing and the Conversion, the Investors, Founders, and Company have agreed to enter into this Agreement.

(l)         “Series A Preferred” means all shares of the Series A-1 Convertible Preferred Stock and Series A-2 Convertible Preferred Stock..

8.4         Amendment. Except as expressly provided herein, neither this Agreement nor any term hereof may be amended, waived, discharged or terminated other than by a written instrument referencing this Agreement and signed by the Company and the Investors holding a majority of the Common Stock issued or issuable upon conversion of the Preferred Stock (excluding any of such shares that have been sold to the public or pursuant to Rule 144); provided, however, that Investors purchasing Shares in a Closing after the Initial Closing (as such terms are defined in the Purchase Agreement) may become parties to this Agreement by executing a counterpart of this Agreement, without any amendment of this Agreement pursuant to this paragraph or any consent or approval of any other Investor; and provided, further, that if any amendment, waiver, discharge or termination operates in a manner that treats any Investor materially different from other Investors, the consent of such Investor shall also be required for such amendment, waiver, discharge or termination; and provided, further, that if any such amendment or waiver shall be to the material detriment of a Seller (when compared to the obligations as to which Seller is already subject to under this Agreement), the consent of such Seller shall also be required. Any such amendment, waiver, discharge or termination effected in accordance with this paragraph shall be binding upon each Seller, each Investor and each future holder of shares of Preferred Stock with rights under this Agreement. Each Investor acknowledges that by the operation of this paragraph, the holders of a majority of the Common Stock issued or issuable upon conversion of the Preferred Stock (excluding any of such shares that have been sold to the public or pursuant to Rule 144) will have the right and power to diminish or eliminate all rights of such Investor under this Agreement.

The parties are signing this Amendment to Right of First Refusal and Co-Sale Agreement as of the date stated in the introductory clause.

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Signature page to Amendment to Right of First Refusal and Co-Sale Agreement of

Cancer Prevention Pharmaceuticals, Inc.