Document:

EX-10.4

 Exhibit 10.4 

AMENDMENT TO 
 SYNDAX
PHARMACEUTICALS, INC. 
 2007 STOCK PLAN 

WHEREAS, by written consent of the board of directors dated as of March 8, 2013 and by written consent of the stockholders dated as of
March 8, 2013, the directors and stockholders of Syndax Pharmaceuticals, Inc. (the “Company”) approved an amendment to the Syndax Pharmaceuticals, Inc. 2007 Stock Plan (the “Plan”) to amend the number of shares
of common stock that may be issued pursuant to awards granted under the Plan from 5,750,000 to 85,511,865; 
 The Plan is hereby amended in
the following respects: 
 Effective as of March 8, 2013, Section 3 of the Plan is amended and restated in its entirety to read as
follows: 
 “3. Stock Subject to the Plan. Subject to the provisions of Section 14 of the Plan, the
maximum aggregate number of Shares that may be sold under the Plan is 85,511,865. The Shares may be authorized, but unissued, or reacquired Common Stock. If an award should expire or become unexercisable for any reason without having been exercised
in full, or is surrendered pursuant to an Option Exchange Program, the unpurchased Shares that were subject thereto shall, unless the Plan shall have been terminated, become available for future grant under the Plan. In addition, any Shares of
Common Stock which are retained by the Company upon exercise of an award in order to satisfy the exercise or purchase price for such award or any withholding taxes due with respect to such exercise or purchase shall be treated as not issued and
shall continue to be available under the Plan. Shares issued under the Plan and later repurchased by the Company pursuant to any repurchase right which the Company may have shall be available for future grant under the Plan.” 

[Signature page follows.] 

 To record the adoption of this Amendment to the Plan, the Company has caused its undersigned
officer to execute this document as of the date first written above. 
  

			
	SYNDAX PHARMACEUTICALS, INC.
		
	By:	 	 /s/ Arlene Morris

	Name:	 	Arlene Morris
	Title:	 	Chief Executive Officer

 [Signature page to Amendment to the Plan.]EX-10.5

 Exhibit 10.5 

AMENDMENT TO 
 SYNDAX
PHARMACEUTICALS, INC. 
 2007 STOCK PLAN 

WHEREAS, by resolutions of the board of directors adopted on July 9, 2013 and by written consent of the stockholders dated as of
July 10, 2013, the directors and stockholders of Syndax Pharmaceuticals, Inc. (the “Company”) approved an amendment to the Syndax Pharmaceuticals, Inc. 2007 Stock Plan (the “Plan”) to amend the number of shares
of common stock that may be issued pursuant to awards granted under the Plan from 85,511,865 to 100,121,865; 
 The Plan is hereby amended
in the following respects: 
 Effective as of July 10, 2013, Section 3 of the Plan is amended and restated in its entirety to read
as follows: 
 “3. Stock Subject to the Plan. Subject to the provisions of Section 14 of the Plan, the maximum
aggregate number of Shares that may be sold under the Plan is 100,121,865. The Shares may be authorized, but unissued, or reacquired Common Stock. If an award should expire or become unexercisable for any reason without having been exercised in
full, or is surrendered pursuant to an Option Exchange Program, the unpurchased Shares that were subject thereto shall, unless the Plan shall have been terminated, become available for future grant under the Plan. In addition, any Shares of Common
Stock which are retained by the Company upon exercise of an award in order to satisfy the exercise or purchase price for such award or any withholding taxes due with respect to such exercise or purchase shall be treated as not issued and shall
continue to be available under the Plan. Shares issued under the Plan and later repurchased by the Company pursuant to any repurchase right which the Company may have shall be available for future grant under the Plan.” 

[Signature page follows.] 

 To record the adoption of this Amendment to the Plan, the Company has caused its undersigned
officer to execute this document as of the date first written above. 
  

			
	SYNDAX PHARMACEUTICALS, INC.
		
	By:	 	 /s/ Arlene Morris

	Name:	 	Arlene Morris
	Title:	 	Chief Executive Officer

 [Signature page to Amendment to the Plan.]EX-10.6

 Exhibit 10.6 

AMENDMENT TO 
 SYNDAX
PHARMACEUTICALS, INC. 
 2007 STOCK PLAN 

WHEREAS, by written consent of the board of directors (the “Board”) of Syndax Pharmaceuticals, Inc. (the
“Company”) adopted on January 17, 2014 and by written consent of the stockholders of the Company dated as of January 23, 2014, the Board and stockholders of the Company approved an amendment to the Company’s 2007
Stock Plan (the “Plan”) to amend the number of shares of the Company’s common stock that may be issued pursuant to awards granted under the Plan from 10,012,178 (which number of shares reserved under the Plan reflects a
1-for-10 reverse stock split of Common Stock effected by the Company on November 18, 2013) to 12,327,178. 
 The Plan is hereby amended
in the following respects: 
 Effective as of January 23, 2014, Section 3 of the Plan is amended and restated in its entirely to
read as follows: 
 “3. Stock Subject to the Plan. Subject to the provisions of Section 14 of the Plan, the maximum
aggregate number of Shares that may be sold under the Plan is 12,327,178. The Shares may be authorized, but unissued, or reacquired Common Stock. If an award should expire or become unexercisable for any reason without having been exercised in full,
or is surrendered pursuant to an Option Exchange Program, the unpurchased Shares that were subject thereto shall, unless the Plan shall have been terminated, become available for future grant under the Plan. In addition, any Shares of Common Stock
which are retained by the Company upon exercise of an award in order to satisfy the exercise or purchase price for such award or any withholding taxes due with respect to such exercise or purchase shall be treated as not issued and shall continue to
be available under the Plan. Shares issued under the Plan and later repurchased by the Company pursuant to any repurchase right which the Company may have shall be available for future grant under the Plan.” 

[Signature Page Follows] 

 To record the adoption of this Amendment to the Plan, the Company has caused its undersigned
officer to execute this document as of the date first written above. 
  

			
	SYNDAX PHARMACEUTICALS, INC.
		
	By:	 	 /s/ Arlene M. Morris

	Name:	 	Arlene M. Morris
	Title:	 	President and Chief Executive OfficerEX-10.7

 Exhibit 10.7 

AMENDMENT TO 
 SYNDAX
PHARMACEUTICALS, INC. 
 2007 STOCK PLAN 

WHEREAS, by resolutions of the board of directors (the “Board”) of Syndax Pharmaceuticals, Inc. (the
“Company”) adopted on December 16, 2014 and by written consent of the stockholders of the Company dated as of December 17, 2014, the Board and stockholders of the Company approved an amendment to the Company’s 2007
Stock Plan (the “Plan”) to amend the number of shares of the Company’s common stock that may be issued pursuant to awards granted under the Plan from 1,002,172 (which number of shares reserved under the Plan reflects a 1-for-10
reverse stock split of Common Stock effected by the Company on November 18, 2013 and a 1-for-12.3 reverse stock split of Common Stock effected by the Company on June 3, 2014) to 1,525,000. 

The Plan is hereby amended in the following respects: 

Effective as of December 17, 2014, Section 3 of the Plan is amended and restated in its entirety to read as follows: 

“3. Stock Subject to the Plan. Subject to the provisions of Section 14 of the Plan, the maximum aggregate number of
Shares that may be sold under the Plan is 1,525,000. The Shares may be authorized, but unissued, or reacquired Common Stock. If an award should expire or become unexercisable for any reason without having been exercised in full, or is surrendered
pursuant to an Option Exchange Program, the unpurchased Shares that were subject thereto shall, unless the Plan shall have been terminated, become available for future grant under the Plan. In addition, any Shares of Common Stock which are retained
by the Company upon exercise of an award in order to satisfy the exercise or purchase price for such award or any withholding taxes due with respect to such exercise or purchase shall be treated as not issued and shall continue to be available under
the Plan. Shares issued under the Plan and later repurchased by the Company pursuant to any repurchase right which the Company may have shall be available for future grant under the Plan.” 

[Signature Page Follows] 

 To record the adoption of this Amendment to the Plan, the Company has caused its undersigned
officer to execute this document as of the date first written above. 
  

			
	SYNDAX PHARMACEUTICALS, INC.
		
	By:	 	 /s/ Arlene M. Morris

	Name:	 	Arlene M. Morris
	Title:	 	President and Chief Executive Officer

 [SIGNATURE PAGE TO 2007 STOCK
PLAN AMENDMENT]EX-10.8

 Exhibit 10.8 

AMENDMENT TO 
 SYNDAX
PHARMACEUTICALS, INC. 
 2007 STOCK PLAN 

WHEREAS, by written consent of the board of directors (the “Board”) of Syndax Pharmaceuticals, Inc. (the
“Company”) adopted on May 26, 2015 and by written consent of the stockholders of the Company dated as of May 28, 2015, the Board and stockholders of the Company approved an amendment to the Company’s 2007 Stock Plan
(the “Plan”) to amend the number of shares of the Company’s common stock that may be issued pursuant to awards granted under the Plan from 1,525,000 (which number of shares reserved under the Plan reflects a 1-for-12.3 reverse
stock split of Common Stock effected by the Company on June 3, 2014) to 2,789,000. 
 The Plan is hereby amended in the following
respects: 
 Effective as of May 28, 2015, Section 3 of the Plan is amended and restated in its entirely to read as follows: 

“3. Stock Subject to the Plan. Subject to the provisions of Section 14 of the Plan, the maximum aggregate number of
Shares that may be sold under the Plan is 2,789,000. The Shares may be authorized, but unissued, or reacquired Common Stock. If an award should expire or become unexercisable for any reason without having been exercised in full, or is surrendered
pursuant to an Option Exchange Program, the unpurchased Shares that were subject thereto shall, unless the Plan shall have been terminated, become available for future grant under the Plan. In addition, any Shares of Common Stock which are retained
by the Company upon exercise of an award in order to satisfy the exercise or purchase price for such award or any withholding taxes due with respect to such exercise or purchase shall be treated as not issued and shall continue to be available under
the Plan. Shares issued under the Plan and later repurchased by the Company pursuant to any repurchase right which the Company may have shall be available for future grant under the Plan.” 

[Signature Page Follows] 

 To record the adoption of this Amendment to the Plan, the Company has caused its undersigned
officer to execute this document as of the date first written above. 
  

			
	SYNDAX PHARMACEUTICALS, INC.
		
	By:	 	 /s/ Michael Metzger

	Name:	 	Michael Metzger
	Title:	 	President and Chief Operating Officer

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