Sierra Oncology (SRRA) SC 13G/A Sierra Oncology, Inc.

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13G

INFORMATION TO BE INCLUDED IN STATEMENTS FILED PURSUANT TO

RULE13d-1(b), (c), AND (d) AND AMENDMENTS THERETO FILED

PURSUANT TO RULE13d-2

(Amendment No. 1)

Sierra Oncology, Inc.

(Name of Issuer)

Common Stock, $0.001 par value per share

(Title of Class of Securities)

82640U107

(CUSIP Number)

December 31, 2018

(Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

☐ Rule13d-1(b)

☐ Rule13d-1(c)

☒ Rule13d-1(d)

(1) The remainder of this cover page shall be filled out for a reporting person’s initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter the disclosures provided in a prior cover page.

The information required in the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

CUSIP No. 82640U107 13G Page  2  of 9 Pages

1	NAMES OF REPORTING PERSONS I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY) New Leaf Biopharma Opportunities I, L.P. (“Biopharma I”)
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS) (a)  ☐        (b)  ☒
3	SEC USE ONLY
4	CITIZENSHIP OR PLACE OF ORGANIZATION Delaware

NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH	5	SOLE VOTING POWER 5,020,446 shares; except that (i) New Leaf BPO Associates I, L.P. (“BPO Associates”), the sole general partner of Biopharma I, may be deemed to have sole power to vote such shares; (ii) New Leaf Venture Management III, L.L.C. (“NLV Management”), the sole general partner of BPO Associates and ultimate general partner of Biopharma I, may be deemed to have sole power to vote such shares; and (iii) each of Ronald Hunt (“Hunt”), Vijay Lathi (“Lathi”) and Liam Ratcliffe (“Ratcliffe”), the managers of NLV Management, may be deemed to have shared power to vote such shares.
	6	SHARED VOTING POWER See response to row 5.
	7	SOLE DISPOSITIVE POWER 5,020,446 shares; except that (i) BPO Associates, the sole general partner of Biopharma I, may be deemed to have sole power to dispose of such shares; (ii) NLV Management, the sole general partner of BPO Associates and ultimate general partner of Biopharma I, may be deemed to have sole power to dispose of such shares; and (iii) each of Hunt, Lathi and Ratcliffe, the managers of NLV Management, may be deemed to have shared power to dispose of such shares.
	8	SHARED DISPOSITIVE POWER See response to row 7.

9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 5,020,446
10	CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES (SEE INSTRUCTIONS) ☐
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9) 6.8%
12	TYPE OF REPORTING PERSON (SEE INSTRUCTIONS) PN

CUSIP No. 82640U107 13G Page  3  of 9 Pages

1	NAMES OF REPORTING PERSONS I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY) New Leaf BPO Associates I, L.P.
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS) (a)  ☐        (b)  ☒
3	SEC USE ONLY
4	CITIZENSHIP OR PLACE OF ORGANIZATION Delaware

NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH	5	SOLE VOTING POWER 5,020,446 shares, all of which are owned by BioPharma I; except that (i) BPO Associates, the sole general partner of Biopharma I, may be deemed to have sole power to vote such shares; (ii) NLV Management, the sole general partner of BPO Associates and ultimate general partner of Biopharma I, may be deemed to have sole power to vote such shares; and (iii) each of Hunt, Lathi and Ratcliffe, the managers of NLV Management, may be deemed to have shared power to vote such shares.
	6	SHARED VOTING POWER See response to row 5.
	7	SOLE DISPOSITIVE POWER 5,020,446 shares, all of which are owned by BioPharma I; except that (i) BPO Associates, the sole general partner of Biopharma I, may be deemed to have sole power to dispose of such shares; (ii) NLV Management, the sole general partner of BPO Associates and ultimate general partner of Biopharma I, may be deemed to have sole power to dispose of such shares; and (iii) each of Hunt, Lathi and Ratcliffe, the managers of NLV Management, may be deemed to have shared power to dispose of such shares.
	8	SHARED DISPOSITIVE POWER See response to row 7.

9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 5,020,446
10	CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES (SEE INSTRUCTIONS) ☐
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9) 6.8%
12	TYPE OF REPORTING PERSON (SEE INSTRUCTIONS) PN

CUSIP No. 82640U107 13G Page  4  of 9 Pages

1	NAMES OF REPORTING PERSONS I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY) New Leaf Venture Management III, L.L.C.
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS) (a)  ☐        (b)  ☒
3	SEC USE ONLY
4	CITIZENSHIP OR PLACE OF ORGANIZATION Delaware

NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH	5	SOLE VOTING POWER 5,020,446 shares, all of which are owned by BioPharma I; except that (i) BPO Associates, the sole general partner of Biopharma I, may be deemed to have sole power to vote such shares; (ii) NLV Management, the sole general partner of BPO Associates and ultimate general partner of Biopharma I, may be deemed to have sole power to vote such shares; and (iii) each of Hunt, Lathi and Ratcliffe, the managers of NLV Management, may be deemed to have shared power to vote such shares.
	6	SHARED VOTING POWER See response to row 5.
	7	SOLE DISPOSITIVE POWER 5,020,446 shares, all of which are owned by BioPharma I; except that (i) BPO Associates, the sole general partner of Biopharma I, may be deemed to have sole power to dispose of such shares; (ii) NLV Management, the sole general partner of BPO Associates and ultimate general partner of Biopharma I, may be deemed to have sole power to dispose of such shares; and (iii) each of Hunt, Lathi and Ratcliffe, the managers of NLV Management, may be deemed to have shared power to dispose of such shares.
	8	SHARED DISPOSITIVE POWER See response to row 7.

9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 5,020,446
10	CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES (SEE INSTRUCTIONS) ☐
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9) 6.8%
12	TYPE OF REPORTING PERSON (SEE INSTRUCTIONS) OO

CUSIP No. 82640U107 13G Page  5  of 9 Pages

1	NAMES OF REPORTING PERSONS I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY) Vijay Lathi
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS) (a)  ☐        (b)  ☒
3	SEC USE ONLY
4	CITIZENSHIP OR PLACE OF ORGANIZATION United States

NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH	5	SOLE VOTING POWER See response to row 6.
	6	SHARED VOTING POWER 5,020,446 shares, all of which are owned by BioPharma I; except that (i) BPO Associates, the sole general partner of Biopharma I, may be deemed to have sole power to vote such shares; (ii) NLV Management, the sole general partner of BPO Associates and ultimate general partner of Biopharma I, may be deemed to have sole power to vote such shares; and (iii) each of Hunt, Lathi and Ratcliffe, the managers of NLV Management, may be deemed to have shared power to vote such shares.
	7	SOLE DISPOSITIVE POWER See response to row 8.
	8	SHARED DISPOSITIVE POWER 5,020,446 shares, all of which are owned by BioPharma I; except that (i) BPO Associates, the sole general partner of Biopharma I, may be deemed to have sole power to dispose of such shares; (ii) NLV Management, the sole general partner of BPO Associates and ultimate general partner of Biopharma I, may be deemed to have sole power to dispose of such shares; and (iii) each of Hunt, Lathi and Ratcliffe, the managers of NLV Management, may be deemed to have shared power to dispose of such shares.

9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 5,020,446
10	CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES (SEE INSTRUCTIONS) ☐
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9) 6.8%
12	TYPE OF REPORTING PERSON (SEE INSTRUCTIONS) IN

CUSIP No. 82640U107 13G Page  6  of 9 Pages

1	NAMES OF REPORTING PERSONS I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY) Ronald Hunt
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS) (a)  ☐        (b)  ☒
3	SEC USE ONLY
4	CITIZENSHIP OR PLACE OF ORGANIZATION United States citizen

NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH	5	SOLE VOTING POWER See response to row 6.
	6	SHARED VOTING POWER 5,020,446 shares, all of which are owned by BioPharma I; except that (i) BPO Associates, the sole general partner of Biopharma I, may be deemed to have sole power to vote such shares; (ii) NLV Management, the sole general partner of BPO Associates and ultimate general partner of Biopharma I, may be deemed to have sole power to vote such shares; and (iii) each of Hunt, Lathi and Ratcliffe, the managers of NLV Management, may be deemed to have shared power to vote such shares.
	7	SOLE DISPOSITIVE POWER See response to row 8.
	8	SHARED DISPOSITIVE POWER 5,020,446 shares, all of which are owned by BioPharma I; except that (i) BPO Associates, the sole general partner of Biopharma I, may be deemed to have sole power to dispose of such shares; (ii) NLV Management, the sole general partner of BPO Associates and ultimate general partner of Biopharma I, may be deemed to have sole power to dispose of such shares; and (iii) each of Hunt, Lathi and Ratcliffe, the managers of NLV Management, may be deemed to have shared power to dispose of such shares.

9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 5,020,446 shares
10	CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES (SEE INSTRUCTIONS) ☐
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9) 6.8%
12	TYPE OF REPORTING PERSON (SEE INSTRUCTIONS) IN

CUSIP No. 82640U107 13G Page  7  of 9 Pages

1	NAMES OF REPORTING PERSONS I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY) Liam Ratcliffe
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS) (a)  ☐        (b)  ☒
3	SEC USE ONLY
4	CITIZENSHIP OR PLACE OF ORGANIZATION United States

NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH	5	SOLE VOTING POWER See response to row 6.
	6	SHARED VOTING POWER 5,020,446 shares, all of which are owned by BioPharma I; except that (i) BPO Associates, the sole general partner of Biopharma I, may be deemed to have sole power to vote such shares; (ii) NLV Management, the sole general partner of BPO Associates and ultimate general partner of Biopharma I, may be deemed to have sole power to vote such shares; and (iii) each of Hunt, Lathi and Ratcliffe, the managers of NLV Management, may be deemed to have shared power to vote such shares.
	7	SOLE DISPOSITIVE POWER See response to row 8.
	8	SHARED DISPOSITIVE POWER 5,020,446 shares, all of which are owned by BioPharma I; except that (i) BPO Associates, the sole general partner of Biopharma I, may be deemed to have sole power to dispose of such shares; (ii) NLV Management, the sole general partner of BPO Associates and ultimate general partner of Biopharma I, may be deemed to have sole power to dispose of such shares; and (iii) each of Hunt, Lathi and Ratcliffe, the managers of NLV Management, may be deemed to have shared power to dispose of such shares.

9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 5,020,446
10	CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES (SEE INSTRUCTIONS) ☐
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9) 6.8%
12	TYPE OF REPORTING PERSON (SEE INSTRUCTIONS) IN

CUSIP No. 82640U107 13G Page  8  of 9 Pages

Schedule 13G

This Amendment No. 1 (“Amendment No. 1”) amends and supplements the Schedule 13G originally filed with the Securities and Exchange Commission (the “SEC”) on February 14, 2018 (the “Original Schedule 13G”) by the Reporting Persons. The “Reporting Persons” are, collectively, New Leaf Biopharma Opportunities I, L.P. (“Biopharma I”), New Leaf BPO Associates I, L.P. (“BPO Associates”), New Leaf Venture Management III, L.L.C. (“NLV Management”), Liam Ratcliffe (“Ratcliffe”), Ronald Hunt (“Hunt”) and Vijay Lathi (“Lathi”). Only those items that are hereby reported are amended; all other items reported in the Original Schedule 13G remain unchanged. Information given in response to each item shall be deemed incorporated by reference in all other items, as applicable. Capitalized terms not defined in this Amendment No. 1 have the meanings ascribed to them in the Original Schedule 13G.

Item 4. Ownership.

(a) Amount beneficially owned:

Biopharma I is the record owner of the 5,020,446 shares of Common Stock (the “Biopharma Shares”). As the sole general partner of Biopharma I, BPO Associates may be deemed to own beneficially the Biopharma Shares. As the sole general partner of BPO Associates and ultimate generate partner of Biopharma I, NLV Management may be deemed to own beneficially the Biopharma Shares. As the individual managers of NLV Management, each of the Managing Directors also may be deemed to own beneficially the Biopharma Shares. Each Reporting Person disclaims beneficial ownership of such shares of Common Stock except for the shares, if any, such Reporting Person holds of record or to the extent of their pecuniary interest therein, if any.

(b) Percent of class:

See line 11 of cover sheets. The percentages set forth on the cover sheet for each Reporting Person are calculated based on 74,365,965 shares of Common Stock reported by the Issuer to be outstanding as of November 6, 2018, as reported on the Issuer’s Form10-Q as filed with the Securities and Exchange Commission on November 8, 2018.

(c) Number of shares as to which the person has:

(i) Sole power to vote or to direct the vote: see line 5 of cover sheets.

(ii) Shared power to vote or to direct the vote: see line 6 of cover sheets.

(iii) Sole power to dispose or to direct the disposition of: see line 7 of cover sheets.

(iv) Shared power to dispose or to direct the disposition of: see line 8 of cover sheets.

CUSIP No. 82640U107 13G Page  9  of 9 Pages

SIGNATURES

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Date: February 12, 2019

NEW LEAF BIOPHARMA OPPORTUNITIES I, L.P.
By:	NEW LEAF BPO ASSOCIATES I, L.P.
	Its General Partner
	By:	NEW LEAF VENTURE MANAGEMENT III, L.L.C.
		Its General Partner
		By:	/s/ Craig L. Slutzkin
			Craig L. Slutzkin
			Chief Financial Officer
NEW LEAF BPO ASSOCIATES I, L.P.
By:	NEW LEAF VENTURE MANAGEMENT III, L.L.C.
	Its General Partner
	By:	/s/ Craig L. Slutzkin
		Craig L. Slutzkin
		Chief Financial Officer
NEW LEAF VENTURE MANAGEMENT III, L.L.C.
By:	/s/ Craig L. Slutzkin
	Craig L. Slutzkin
	Chief Financial Officer
*
Vijay Lathi
*
Ronald Hunt
*
Liam Ratcliffe

/s/ Craig L. Slutzkin

* Craig L. Slutzkin

Asattorney-in-fact

* This Schedule 13G was executed by Craig L. Slutzkin on behalf of the individuals listed above pursuant to Powers of Attorney. Note that copies of the applicable Powers of Attorney are already on file with the appropriate agencies.