EX-4.2





 Exhibit 4.2 

SIERRA ONCOLOGY, INC. 

SERIES B WARRANT TO PURCHASE COMMON STOCK 
  

					
		  		  	Number of Warrants:
	 Warrant No.: [    ]
	  		  	Number of Warrant Shares:

 Date of Issuance: November [    ], 2019 (“Issuance Date”) 

Expiration Date: Seventy-fifth (75th) day anniversary of the Company’s (as defined below) announcement, via publicly disseminated press release or
SEC filing, of the top-line data results from MOMENTUM, its planned Phase 3 clinical trial of momelotinib for patients with myelofibrosis (“Expiration Date”) 

Sierra Oncology, Inc., a Delaware corporation (the “Company”), certifies that, for good and valuable consideration, the receipt and
sufficiency of which are acknowledged, [    ], the registered holder hereof or its permitted assigns (the “Holder”), is entitled, subject to the terms set forth below, to purchase from the Company, at
the Exercise Price (as defined below) then in effect, upon surrender of this Warrant to Purchase Common Stock (including any Warrants to Purchase Common Stock issued in exchange, transfer or replacement hereof, the “Warrant”), at
any time or times on or after the Exercisability Date, but not after 5:30 p.m., New York Time, on the Expiration Date, [__] fully paid and nonassessable shares of Common Stock (as defined below), equal to the number of Warrants given above
multiplied by 0.33 (the “Warrant Shares”). Except as otherwise defined herein, capitalized terms in this Warrant shall have the meanings set forth in Section 15. This Warrant is one of the warrants to purchase common stock
issued in connection with the transactions contemplated by (i) that certain Underwriting Agreement, dated as of November 7, 2019 by and between the Company and Jefferies LLC as the representative of the several underwriters named therein,
(ii) the Company’s Registration Statement on Form S-3 (File number 333-225650), and (iii) the Company’s prospectus supplement dated as of
November 7, 2019 (the “Offering”). 
 1. EXERCISE OF WARRANT. 

(a) Mechanics of Exercise. Subject to the terms and conditions hereof (including, without limitation, the limitations set forth in
Section 1(d)), this Warrant may be exercised by the Holder on any day on or after the Exercisability Date, in whole or in part (but not as to fractional shares), by delivery of a written notice (which may be by facsimile or email), in the form
attached hereto as Exhibit A (the “Exercise Notice”), of the Holder’s election to exercise this Warrant and payment to the Company of an amount equal to the applicable Exercise Price multiplied by the
number of Warrant Shares as to which this Warrant is being exercised (the “Aggregate Exercise Price”) in cash or wire transfer of immediately available funds. The Holder shall not be required to surrender this Warrant in order to
effect an exercise hereunder; provided, that in the event of an exercise of this Warrant for all Warrant Shares then issuable hereunder, this Warrant is surrendered to the Company’s transfer agent through DTC’s Deposit Withdrawal
Agent Commission system (“DWAC System”) by the second (2nd) Trading Day following the date on which the Company’s transfer agent for the Common Stock and Warrants (“Transfer Agent”) has received the Exercise
Notice. Within one (1) Trading Day following the date of exercise as aforesaid, the Holder shall deliver the Aggregate Exercise Price for the shares specified in the applicable Exercise Notice by wire transfer or cashier’s check drawn
on a United States bank. No ink-original Exercise Notice shall be required, nor shall any medallion guarantee (or other type of guarantee or notarization) of any Exercise Notice form be required, except
as may be required by the Company’s transfer agent. On or before the first (1st) Trading Day following the date on which the Company or the Transfer Agent has received the Exercise Notice, the Company or the Transfer Agent shall transmit
by email or facsimile an acknowledgment of confirmation of receipt of the Exercise Notice to the Holder and the Transfer Agent. The Company or the Transfer Agent shall deliver any objection to the Exercise Notice on or before the first (1st) Trading
Day following the date on which the Company or the Transfer Agent has received the Exercise Notice. In the event of any discrepancy or dispute, the records of the Company and the Transfer Agent shall be controlling and determinative in the absence
of manifest error. On or before the earlier of (i) the third (3rd) Trading Day and (ii) the number of Trading Days comprising the Standard Settlement Period (as defined below) following the date on which the Holder has delivered to the
Company a duly completed and executed Exercise Notice (the “Share Delivery Date”), and the Aggregate Exercise Price, the Company or its Transfer Agent shall, upon the request of the Holder, credit such aggregate number of shares of
Common Stock to which the Holder is entitled pursuant to such exercise to the Holder’s or its designee’s balance account with The Depository Trust Company (“DTC”) through its Deposit Withdrawal At Custodian system. Upon













 
delivery of the Exercise Notice and the Aggregate Exercise Price, the Holder shall be deemed for all corporate purposes to have become the holder of record of the Warrant Shares with respect to
which this Warrant has been exercised, irrespective of the date such Warrant Shares are credited to the Holder’s DTC account or the date of delivery of the book-entry accounts evidencing such Warrant Shares, as the case may be. The Company
agrees to maintain a transfer agent that is a participant in the FAST Program so long as this Warrant remains outstanding and exercisable. As used herein, “Standard Settlement Period” means the standard settlement period,
expressed in a number of Trading Days, on the Principal Market with respect to the Common Stock as in effect on the date of delivery of the Exercise Notice. 

If this Warrant is submitted in connection with any exercise pursuant to this Section 1(a) and the number of Warrant Shares
represented by this Warrant submitted for exercise is greater than the number of Warrant Shares being acquired upon an exercise, then the Transfer Agent shall as soon as practicable and in no event later than ten (10) Trading Days after any
exercise and at its own expense, issue a new Warrant (in accordance with Section 7(e)) representing the right to purchase the number of Warrant Shares purchasable immediately prior to such exercise under this Warrant, less the number of Warrant
Shares with respect to which this Warrant is exercised, through the DWAC System. The Company shall pay any and all taxes that may be payable with respect to the issuance and delivery of Warrant Shares upon exercise of this Warrant; provided,
however, that the Company shall not be required to pay any tax which may be payable based on the income of the Holder or in respect of any transfer involved in the registration of any book-entry accounts for Warrant Shares or Warrants in a
name other than that of the Holder or an affiliate thereof. The Holder shall be responsible for all other tax liability that may arise as a result of holding or transferring this Warrant or receiving Warrant Shares upon exercise hereof. 

If the Company shall fail for any reason or for no reason to credit the Holder’s balance account with DTC for such number of shares of
Common Stock to which the Holder is entitled upon the Holder’s exercise of this Warrant, then the Holder shall be entitled, but not required, to rescind the previously submitted Exercise Notice and the Company or the Transfer Agent shall return
all consideration paid by Holder for such shares upon such rescission. Notwithstanding anything herein to the contrary, the Company shall not be required to make any cash payments to the Holder in lieu of issuance of the Warrant Shares. 

(b) Exercise Price. For purposes of this Warrant, “Exercise Price” means $0.33 per share of Common Stock, subject to
adjustment as provided herein. 
 (c) Reserved. 

(d) Limitations on Exercises. Subject to the last sentence of this Section 1(d), the Company shall not effect the exercise of this
Warrant, and the Holder shall not have the right to exercise this Warrant, to the extent that after giving effect to such exercise, such Holder (together with such Holder’s affiliates and any other Persons acting as a group together) would
beneficially own in excess of 9.99% (the “Maximum Percentage”) of the shares of Common Stock outstanding immediately after giving effect to such exercise. For purposes of the foregoing sentence, the aggregate number of shares of
Common Stock beneficially owned by such Person and its affiliates shall include the number of shares of Common Stock issuable upon exercise of this Warrant with respect to which the determination of such sentence is being made, but shall exclude
shares of Common Stock which would be issuable upon (i) exercise of the remaining, unexercised portion of this Warrant beneficially owned by such Person and its affiliates and (ii) exercise or conversion of the unexercised or unconverted
portion of any other securities of the Company beneficially owned by such Person and its affiliates (including, without limitation, any convertible notes or convertible preferred stock or warrants) subject to a limitation on conversion or exercise
analogous to the limitation contained herein. For purposes of this Warrant, in determining the number of outstanding shares of Common Stock, the Holder may rely on the number of outstanding shares of Common Stock as reflected in (1) the
Company’s most recent Form 10-K, Proxy Statement, Form 10-Q, Current Report on Form 8-K or other public
filing with the Securities and Exchange Commission, as the case may be, (2) a more recent public announcement by the Company or (3) any other notice by the Company or the Transfer Agent setting forth the number of shares of Common Stock
outstanding. For any reason at any time, upon the written or oral request of the Holder, where such request indicates that it is being made pursuant to this Warrant, the Company shall within one (1) Trading Day confirm orally and in writing to
the Holder the number of shares of Common Stock then outstanding. In any case, the number of outstanding shares of Common Stock shall be determined after giving effect to the conversion or exercise of securities of the Company, including the
Warrants, by the Holder and its affiliates since the date as of 

  
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which such number of outstanding shares of Common Stock was reported. Upon delivery of a written notice to the Company, the Holder may from time to time increase or decrease the Maximum
Percentage to any other percentage as specified in such notice; provided that (i) any such increase in the Maximum Percentage will not be effective until the sixty-first (61st) day after such notice is delivered to the Company and (ii) any
such increase or decrease will apply only to the Holder and not to any other holder of Warrants. For purposes of clarity, the shares of Common Stock issuable pursuant to the terms of this Warrant in excess of the Maximum Percentage shall not be
deemed to be beneficially owned by the Holder for any purpose including for purposes of Section 13(d) or Rule 16a-1(a)(1) of the Exchange Act. No prior inability to exercise this Warrant pursuant to this
paragraph shall have any effect on the applicability of the provisions of this paragraph with respect to any subsequent determination of exercisability. The provisions of this paragraph shall be construed and implemented in a manner otherwise than
in strict conformity with the terms of this Section 1(d) to the extent necessary to correct this paragraph or any portion of this paragraph which may be defective or inconsistent with the intended beneficial ownership limitation contained in
this Section 1(d) or to make changes or supplements necessary or desirable to properly give effect to such limitation. The limitations set forth in this Section 1(d) shall not apply to exercises of this Warrant that occur prior to and
expressly in connection with the Company’s consummation of a Fundamental Transaction. 
 (e) No Fractional Shares or Scrip. No
fractional shares or scrip representing fractional shares shall be issued upon the exercise of this Warrant. As to any fraction of a share that the Holder would otherwise be entitled to purchase upon such exercise, the Company shall pay a cash
adjustment in respect of such final fraction in an amount equal to such fraction multiplied by the Exercise Price. 
 2. ADJUSTMENT OF
EXERCISE PRICE AND NUMBER OF WARRANT SHARES. The Exercise Price and the number of Warrant Shares shall be adjusted from time to time as follows: 

(a) Adjustment upon Subdivision or Combination of Shares of Common Stock. If the Company at any time on or after the Issuance Date
subdivides (by any stock split, stock dividend, recapitalization or otherwise) one or more classes of its outstanding shares of Common Stock into a greater number of shares, the Exercise Price in effect immediately prior to such subdivision will be
proportionately reduced and the number of Warrant Shares will be proportionately increased. If the Company at any time on or after the Issuance Date combines (by combination, reverse stock split or otherwise) one or more classes of its outstanding
shares of Common Stock into a smaller number of shares, the Exercise Price in effect immediately prior to such combination will be proportionately increased and the number of Warrant Shares will be proportionately decreased. Any adjustment under
this Section 2(a) shall become effective at the close of business on the date the subdivision or combination becomes effective. 

(b) [Reserved.] 
 (c)
Par Value. Notwithstanding anything to the contrary in this Warrant, in no event shall the Exercise Price be reduced below the par value of the Company’s Common Stock. 

3. RIGHTS UPON DISTRIBUTION OF ASSETS. If the Company shall declare or make any dividend or other distribution of its assets (or rights
to acquire its assets) to holders of shares of Common Stock, by way of return of capital or otherwise (including, without limitation, any distribution of cash, stock or other securities, property or options by way of a dividend, spin off,
reclassification, corporate rearrangement, scheme of arrangement or other similar transaction) (a “Distribution”), at any time after the issuance of this Warrant, then, in each such case: 

(a) any Exercise Price in effect immediately prior to the close of business on the record date fixed for the determination of holders of shares
of Common Stock entitled to receive the Distribution shall be reduced, effective as of the close of business on such record date, to a price determined by multiplying such Exercise Price by a fraction of which (i) the numerator shall be the
Weighted Average Price of the shares of Common Stock on the Trading Day immediately preceding such record date minus the value of the Distribution (as determined in good faith by the Company’s Board of Directors) applicable to one share of
Common Stock, and (ii) the denominator shall be the Weighted Average Price of the shares of Common Stock on the Trading Day immediately preceding such record date; and 

  
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 (b) the number of Warrant Shares shall be increased to a number of shares equal to the
number of shares of Common Stock obtainable immediately prior to the close of business on the record date fixed for the determination of holders of shares of Common Stock entitled to receive the Distribution multiplied by the reciprocal of the
fraction set forth in the immediately preceding paragraph (a). 
 4. PURCHASE RIGHTS; FUNDAMENTAL TRANSACTIONS. 

(a) Purchase Rights. In addition to any adjustments pursuant to Section 2 above, if at any time prior to the Expiration Date, the
Company grants, issues or sells any Options, Convertible Securities or rights to purchase stock, warrants, securities or other property pro rata to all of the record holders of any class of shares of Common Stock (the “Purchase
Rights”), then the Holder will be entitled to acquire, upon the terms applicable to such Purchase Rights, the aggregate Purchase Rights which the Holder could have acquired if the Holder had held the number of shares of Common Stock
acquirable upon complete exercise of this Warrant (without regard to any limitations on the exercise of this Warrant) immediately before the date on which a record is taken for the grant, issuance or sale of such Purchase Rights, or, if no such
record is taken, the date as of which the record holders of shares of Common Stock are to be determined for the grant, issue or sale of such Purchase Rights.

(b) Fundamental Transactions. The Company shall not enter into or be party to a Fundamental Transaction unless (i) if the successor
entity is a publicly traded corporation whose common stock is quoted on or listed for trading on an Eligible Market, the successor entity assumes in writing all of the obligations of the Company under this Warrant pursuant to written agreements in
form and substance reasonably satisfactory to the Majority Holders, including agreements to deliver to each Holder of Warrants in exchange for such Warrants a written instrument issued by the successor entity substantially similar in form and
substance to this Warrant, including, without limitation, an adjusted Exercise Price equal to the value for the shares of Common Stock reflected by the terms of such Fundamental Transaction, and exercisable for a corresponding number of shares of
capital stock equivalent to the shares of Common Stock acquirable and receivable upon exercise of this Warrant (without regard to any limitations on the exercise of this Warrant) prior to such Fundamental Transaction, and reasonably satisfactory to
the Majority Holders and (ii) if the successor entity is not a publicly traded corporation whose common stock is quoted on or listed for trading on an Eligible Market, the successor entity assumes in writing all of the obligations of the
Company under this Warrant pursuant to written agreements in form and substance reasonably satisfactory to the Majority Holders, including agreements to deliver to each holder of Warrants in exchange for such Warrants a written instrument issued by
the successor entity substantially similar in form and substance to this Warrant exercisable for the consideration that would have been issuable in the Fundamental Transaction in respect of the Warrant Shares had this Warrant been exercised
immediately prior to the consummation of the Fundamental Transaction. The provisions of this Section 4(b) shall apply similarly and equally to successive Fundamental Transactions and shall be applied without regard to any limitations on the
exercise of this Warrant. Notwithstanding the foregoing, in the event of a Fundamental Transaction other than pursuant to clause (i) above, then, at the request of the Majority Holders delivered before the 30th day after such Fundamental
Transaction, the Company (or the successor entity) shall purchase this Warrant and all other outstanding Warrants from the Holders by paying to the Holders, within five (5) business days after such request (or, if later, on the effective date
of the Fundamental Transaction), cash in an amount equal to the Black Scholes Value of the remaining unexercised portion of each Warrant, as applicable, on the date of such Fundamental Transaction. For the sake of clarity, such calculation shall
assume full exercisability of this Warrant (e.g. without regard to any limitations on the exercise of this Warrant, including those set forth in Sections 1(d) and 5(b)). 

5. RESERVATION OF WARRANT SHARES. 

(a) The Company covenants that it will at all times after the Exercisability Date reserve and keep available out of the aggregate of its
authorized but unissued and otherwise unreserved Common Stock, solely for the purpose of enabling it to issue Warrant Shares upon exercise of this Warrant as herein provided, the number of shares of Common Stock which are then issuable and
deliverable upon the exercise of this entire Warrant, free from preemptive or any other contingent purchase rights of Persons other than the Holder (taking into account the adjustments and restrictions in Section 2). Such reservation shall
comply without regard to the provisions of Section 1(d). The Company covenants that all shares of Common Stock so issuable and deliverable shall be, upon issuance and the payment of the applicable Exercise Price in accordance with the terms
hereof, duly authorized, 

  
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validly issued and fully paid and nonassessable. The Company will take all such actions as may be reasonably necessary to ensure that such shares of Common Stock may be issued as provided herein
without violation of any applicable law or regulation, or of any requirements of any securities exchange or automated quotation system upon which the Common Stock may be listed. 

(b) Following the Issuance Date, the Company covenants and agrees that it will use reasonable best efforts to obtain approval by the
Company’s stockholders, at the first meeting of stockholders following the Issuance Date, which the Company shall use best efforts to hold as soon as practicable after the Issuance Date, but not later than 75 days from the Issuance Date (which
shall be extended to 120 days from the Issuance Date in the event that the Company receives comments to the preliminary proxy statement for such meeting from the Securities and Exchange Commission), of an amendment to the Company’s certificate
of incorporation increasing the aggregate number of authorized shares of Common Stock such that the Company shall have sufficient authorized but unissued and otherwise unreserved shares of Common Stock, solely for the purpose of enabling it to issue
Warrant Shares upon exercise of this Warrant as herein provided, without regard to the provisions of Section 1(d) (the “Proposal”). The Company covenants and agrees that its Board of Directors shall unanimously
recommend that the Proposal be approved by the Company’s stockholders at all meetings in which such Proposal is considered and promptly file the necessary amendments to the Company’s certificate of incorporation after the Proposal is
approved. If the Company’s stockholders do not approve such Proposal at the first meeting in which it is voted on by stockholders, the Company covenants and agrees that it will submit the Proposal for approval of the Company’s
stockholders at least annually until such approval is obtained. 
 6. WARRANT HOLDER NOT DEEMED A SHAREHOLDER. Except as otherwise
specifically provided herein, the Holder, solely in such Person’s capacity as a holder of this Warrant, shall not be entitled to vote or receive dividends or be deemed the holder of share capital of the Company for any purpose, nor shall
anything contained in this Warrant be construed to confer upon the Holder, solely in such Person’s capacity as the Holder of this Warrant, any of the rights of a shareholder of the Company or any right to vote, give or withhold consent to any
corporate action (whether any reorganization, issue of stock, reclassification of stock, consolidation, merger, conveyance or otherwise), receive notice of meetings, receive dividends or subscription rights, or otherwise, prior to the issuance to
the Holder of the Warrant Shares which such Person is then entitled to receive upon the due exercise of this Warrant. In addition, nothing contained in this Warrant shall be construed as imposing any liabilities on the Holder to purchase any
securities (upon exercise of this Warrant or otherwise) or as a shareholder of the Company, whether such liabilities are asserted by the Company or by creditors of the Company. 

7. REGISTRATION AND REISSUANCE OF WARRANTS. 

(a) Registration of Warrant. The Company or its Transfer Agent shall register this Warrant, upon the records to be maintained by the
Company for that purpose (the “Warrant Register”), in the name of the record Holder hereof from time to time. The Company and its Transfer Agent may deem and treat the registered Holder of this Warrant as the absolute owner hereof
for the purpose of any exercise hereof or any distribution to the Holder, and for all other purposes, absent actual notice to the contrary. The Company and its Transfer Agent shall also register any transfer, exchange, reissuance or cancellation of
any portion of this Warrant in the Warrant Register. 
 (b) Transfer of Warrant. This Warrant may be offered for sale, sold,
transferred or assigned without the consent of the Company, except as may otherwise be required by applicable securities laws. Subject to applicable securities laws, if this Warrant is to be transferred, the Holder shall surrender this Warrant to
the Company or its Transfer Agent, as directed by the Company, together with all applicable transfer taxes, whereupon the Company will, or will cause its Transfer Agent to, forthwith issue and deliver upon the order of the Holder a new Warrant (in
accordance with Section 7(e)), registered as the Holder may request, representing the right to purchase the number of Warrant Shares being transferred by the Holder and, if less than the total number of Warrant Shares then underlying this
Warrant is being transferred, a new Warrant (in accordance with Section 7(e)) to the Holder representing the right to purchase the number of Warrant Shares not being transferred. The acceptance of the new Warrant by the transferee thereof shall
be deemed the acceptance by such transferee of all of the rights and obligations in respect of the new Warrant that the Holder has in respect of this Warrant. 

  
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 (c) Lost, Stolen or Mutilated Warrant. Upon receipt by the Company 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, of any indemnification undertaking by the Holder to the Company in customary form (which shall not
include the posting of any bond) and, in the case of mutilation, upon surrender and cancellation of this Warrant, the Company or its Transfer Agent, as directed by the Company, shall execute and deliver to the Holder a new Warrant (in accordance
with Section 7(e)) representing the right to purchase the Warrant Shares then underlying this Warrant. 
 (d) Exchangeable for
Multiple Warrants. This Warrant is exchangeable, upon the surrender hereof by the Holder at the principal office of the Company or its Transfer Agent, as directed by the Company, together with all applicable transfer taxes, for a new Warrant or
Warrants (in accordance with Section 7(e)) representing in the aggregate the right to purchase the number of Warrant Shares then underlying this Warrant, and each such new Warrant will represent the right to purchase such portion of such
Warrant Shares as is designated by the Holder at the time of such surrender; provided, however, that the Company or its Transfer Agent, as directed by the Company, shall not be required to issue Warrants for fractional shares of Common
Stock hereunder. 
 (e) Issuance of New Warrants. Whenever the Company or its Transfer Agent, as directed by the Company, is required
to issue a new Warrant pursuant to the terms of this Warrant, such new Warrant shall (i) be of like tenor with this Warrant, (ii) represent, as indicated on the face of such new Warrant, the right to purchase the Warrant Shares then
underlying this Warrant (or in the case of a new Warrant being issued pursuant to Section 7(b) or Section 7(c), the Warrant Shares designated by the Holder which, when added to the number of shares of Common Stock underlying the other
new Warrants issued in connection with such issuance, does not exceed the number of Warrant Shares then underlying this Warrant), (iii) have an issuance date, as indicated on the face of such new Warrant, which is the same as the Issuance Date
and (iv) have the same rights and conditions as this Warrant.
 8. NOTICES. Whenever notice is required to be given under this
Warrant, unless otherwise provided herein, such notice shall be given in accordance with the information set forth in the Warrant Register. The Company shall give written notice to the Holder (i) reasonably promptly following any adjustment of
the Exercise Price, setting forth in reasonable detail the calculation of such adjustment and (ii) at least ten (10) days prior to the date on which the Company closes its books or takes a record (A) with respect to any dividend or
distribution upon the shares of Common Stock, (B) with respect to any grants, issuances or sales of any Options, Convertible Securities or rights to purchase stock, warrants, securities or other property pro rata to the record holders of any
class of shares of Common Stock or (C) for determining rights to vote with respect to any Fundamental Transaction, dissolution or liquidation; provided, that in each case, the Company will only be required to provide such information to
the Holder if such information shall have been made known to the public prior to or in conjunction with such notice being provided to the Holder. 

9. AMENDMENT AND WAIVER. This Warrant may be modified or amended or the provisions hereof waived with the written consent of the
Company and the Majority Holders. Any amendment, modification or waiver effected in the accordance with the foregoing shall be binding on all Warrants and holders thereof. 

10. LIMITATION OF LIABILITY. No provision hereof, in the absence of any affirmative action by Holder to exercise this Warrant to
purchase Warrant Shares, and no enumeration herein of the rights or privileges of Holder, shall give rise to any liability of Holder for the purchase price of any Warrant Shares or as a shareholder of the Company, whether such liability is asserted
by the Company or by creditors of the Company. 
 11. GOVERNING LAW. This Warrant shall be governed by and construed and enforced in
accordance with, and all questions concerning the construction, validity, interpretation and performance of this Warrant shall be governed by, the internal laws of the State of New York, without giving effect to any choice of law or conflict of law
provision or rule (whether of the State of New York or any other jurisdictions) that would cause the application of the laws of any jurisdictions other than the State of New York. 

12. CONSTRUCTION; HEADINGS. This Warrant shall be deemed to be jointly drafted by the Company and the Holder and shall not be construed
against any Person as the drafter hereof. The headings of this Warrant are for convenience of reference and shall not form part of, or affect the interpretation of, this Warrant. 

  
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 13. DISPUTE RESOLUTION. In the case of a dispute as to the determination of the
Exercise Price or the arithmetic calculation of the Warrant Shares, the Company shall submit the disputed determinations or arithmetic calculations via email or facsimile within five (5) Trading Days of receipt of the Exercise Notice giving
rise to such dispute, as the case may be, to the Holder. If the Holder and the Company are unable to agree upon such determination or calculation of the Exercise Price or the Warrant Shares within five (5) Trading Days of such disputed
determination or arithmetic calculation being submitted to the Holder, then the Company shall, within two (2) Trading Days thereafter submit via email or facsimile (a) the disputed determination of the Exercise Price to an
independent, reputable investment bank selected by the Company and approved by the Holder or (b) the disputed arithmetic calculation of the Warrant Shares to the Company’s independent, outside accountant. The Company shall cause the
investment bank or the accountant, as the case may be, to perform the determinations or calculations and notify the Company and the Holder of the results no later than twenty (20) Trading Days from the time it receives the disputed
determinations or calculations. Such investment bank’s or accountant’s determination or calculation, as the case may be, shall be binding upon all parties absent demonstrable error. The expenses of the investment bank and accountant will
be borne by the Company unless the investment bank or accountant determines that the determination of the Exercise Price or the arithmetic calculation of the Warrant Shares by the Holder was incorrect by more than 25%, in which case the expenses of
the investment bank and accountant will be borne by the Holder. 
 14. REMEDIES, OTHER OBLIGATIONS, BREACHES AND INJUNCTIVE RELIEF.
The remedies provided in this Warrant shall be cumulative and in addition to all other remedies available under this Warrant, at law or in equity (including a decree of specific performance and/or other injunctive relief), and nothing herein shall
limit the right of the Holder to pursue actual damages for any failure by the Company to comply with the terms of this Warrant. The Company acknowledges that a breach by it of its obligations hereunder may cause irreparable harm to the Holder and
that the remedy at law for any such breach may be inadequate. The Company therefore agrees that, in the event of any such breach or threatened breach, the holder of this Warrant shall be entitled, in addition to all other available remedies, to seek
an injunction restraining any breach. Notwithstanding the foregoing or anything else herein to the contrary, if the Company is for any reason unable to issue and deliver Warrant Shares upon exercise of this Warrant as required pursuant to the terms
hereof, the Company shall have no obligation to pay to the Holder any cash or other consideration or otherwise “net cash settle” this Warrant. 

15. CERTAIN DEFINITIONS. For purposes of this Warrant, the following terms shall have the following meanings: 

(a) “Black Scholes Value” means the value of this Warrant based on the Black and Scholes Option Pricing Model obtained from
the “OV” function on Bloomberg determined as of the day immediately following the public announcement of the applicable Fundamental Transaction and reflecting (i) a risk-free interest rate corresponding to the U.S. Treasury rate for a
period equal to the remaining term of this Warrant as of such date of request and (ii) an expected volatility equal to the greater of 80% and the 100-day volatility obtained from the HVT function on
Bloomberg. 
 (b) “Bloomberg” means Bloomberg Financial Markets. 

(c) “Common Stock” means (i) the Company’s shares of Common Stock, $0.001 par value per share, and (ii) any
share capital into which such Common Stock shall have been changed or any share capital resulting from a reclassification of such Common Stock. 

(d) “Convertible Securities” means any stock or securities (other than Options) directly or indirectly convertible into or
exercisable or exchangeable for shares of Common Stock. 
 (e) “Eligible Market” means the NYSE MKT LLC, The New York Stock
Exchange, Inc., The Nasdaq Stock Market, or the OTC Bulletin Board®. 
 (f)
“Exchange Act” means the Securities Exchange Act of 1934, as amended. 

  
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 (g) “Exercisability Date” means the later of (i) the Issuance Date and
(ii) the first Trading Day following the date the Company obtains shareholder approval for the Proposal as described in Section 5(b) above; provided, however, in the event of a Fundamental Transaction prior to obtaining shareholder
approval of the Proposal, the first Trading Day following the closing of the Fundamental Transaction shall be deemed the Exercisability Date; provided, further, that treatment of this Warrant in the event of a Fundamental Transaction is addressed in
Section 4(b) above. 
 (h) “Fundamental Transaction” means that (A) the Company shall, directly or indirectly, in
one or more related transactions, (i) consolidate or merge with or into (whether or not the Company is the surviving corporation) another Person, or (ii) sell, assign, transfer, convey or otherwise dispose of all or substantially all of
the properties or assets of the Company to another Person, or (iii) allow another Person to make a purchase, tender or exchange offer that is accepted by the holders of more than 50% of the outstanding shares of Common Stock (not including any
shares of Common Stock held by the Person or Persons making or party to, or associated or affiliated with the Persons making or party to, such purchase, tender or exchange offer), or (iv) consummate a stock purchase agreement or other business
combination (including, without limitation, a reorganization, recapitalization, spin-off or scheme of arrangement) with another Person whereby such other Person acquires more than 50% of the outstanding shares
of Common Stock (not including any shares of Common Stock held by the other Person or other Persons making or party to, or associated or affiliated with the other Persons making or party to, such stock purchase agreement or other business
combination) or (B) any “person” or “group” (as these terms are used for purposes of Sections 13(d) and 14(d) of the Exchange Act) is or shall become the “beneficial owner” (as defined in Rule 13d-3 under the Exchange Act), directly or indirectly, of more than 50% of the aggregate ordinary voting power represented by issued and outstanding Common Stock. 

(i) “Majority Holders” means the holders of a majority of the Warrant Shares underlying the then outstanding Warrants
(disregarding for this purpose any and all limitations of any kind on exercise of any Warrants). 
 (j) “Options” means any
rights, warrants or options to subscribe for or purchase shares of Common Stock or Convertible Securities. 
 (k) “Person”
means an individual, a limited liability company, a partnership, a joint venture, a corporation, a trust, an unincorporated organization, any other entity and a government or any department or agency thereof. 

(l) “Principal Market” means (i) the Nasdaq Global Market, or (ii) if the Nasdaq Global Market is not the principal
trading market for the Common Stock, then the principal securities exchange or securities market on which the Common Stock is then traded. 

(m) “Securities Act” means the Securities Act of 1933, as amended. 

(n) “Trading Day” means any day on which the Common Stock is traded on the Principal Market. 

(o) [Reserved.] 
 (p)
“Weighted Average Price” means, for any security as of any date, the dollar volume-weighted average price for such security on the Principal Market during the period beginning at 9:30:01 a.m., New York City time, and ending at
4:00:00 p.m., New York City time, as reported by Bloomberg through its “Volume at Price” function or, if the foregoing does not apply, the dollar volume-weighted average price of such security in the over-the-counter market on the electronic bulletin board for such security during the period beginning at 9:30:01 a.m., New York City time, and ending at 4:00:00 p.m., New York City time, as reported by
Bloomberg, or, if no dollar volume-weighted average price is reported for such security by Bloomberg for such hours, the average of the highest closing bid price and the lowest closing ask price of any of the market makers for such security as
reported in the “pink sheets” by Pink OTC Markets Inc. If the Weighted Average Price cannot be calculated for such security on such date on any of the foregoing bases, the Weighted Average Price of such security on such date shall be the


  
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fair market value as mutually determined by the Company and the Holder. If the Company and the Holder are unable to agree upon the fair market value of such security, then such dispute shall be
resolved pursuant to Section 13 with the term “Weighted Average Price” being substituted for the term “Exercise Price.” All such determinations shall be appropriately adjusted for any share dividend, share split or other
similar transaction during such period. 
 [Signature Page Follows]

  
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 IN WITNESS WHEREOF, the Company has caused this Warrant to Purchase Common Stock to
be duly executed as of the Issuance Date set out above. 
  

			
	SIERRA ONCOLOGY, INC.


 
			
		
	By:	 	  



 
			
	(Signature)
	
	Name: Sukhi Jagpal
	
	Title: Chief Financial Officer



  
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 EXHIBIT A 

EXERCISE NOTICE 
 TO BE
EXECUTED BY THE REGISTERED HOLDER TO EXERCISE THIS 
 WARRANT TO PURCHASE COMMON STOCK 

SIERRA ONCOLOGY, INC. 
 The undersigned
holder hereby exercises the right to purchase                 of the shares of Common Stock (“Warrant Shares”) of Sierra Oncology, Inc., a Delaware
corporation (the “Company”), evidenced by the attached Warrant to Purchase Common Stock (the “Warrant”). Capitalized terms used herein and not otherwise defined shall have the respective meanings set forth in the
Warrant. 
 1. Exercise Price. The Holder shall pay the sum of
$                to the Company in accordance with the terms of the Warrant. 

2. Delivery of Warrant Shares. The Company shall deliver to the holder
                Warrant Shares in accordance with the terms of the Warrant. 

3. Representations and Warranties. By its delivery of this Exercise Notice, the undersigned represents and warrants to the Company that
in giving effect to the exercise evidenced hereby the Holder will not beneficially own in excess of the number of shares of Common Stock (determined in accordance with Section 13(d) of the Securities Exchange Act of 1934, as amended)
permitted to be owned under Section 1(d) of this Warrant to which this notice relates. 
  

			
	DATED:                     	  	
		
		  	(Signature must conform in all respects to name of the Holder as specified on the face of the Warrant)
		  	  

		  	Registered Holder
		
		  	Address:


  
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