EX-10.21



 Exhibit 10.21 
  

			
	 




	  	Confidential Materials omitted and filed separately with the Securities and Exchange Commission. Double asterisks denote omissions.

 215 First St, Suite 200 

Cambridge, MA 02142 
 July 6, 2017 

Adrian Senderowicz, MD 
 Dear Adrian, 

As we have discussed, Constellation Pharmaceuticals, Inc. (“the Company”) is impressed with the skills you have exhibited and would
like to expand your engagement with the Company. The Company is therefore pleased to extend to you this offer of employment as its Chief Medical Officer. Please note that by accepting this offer, you are agreeing that the May 2, 2017 consulting
agreement between you and the Company (the “Consulting Agreement”) will terminate, effective as of your start date. On behalf of the Company, I have set forth below the terms of your employment should you accept our offer: 

Employment: You will be employed to serve on a full-time basis in the position of Senior Vice President & Chief Medical Officer, reporting to
the Chief Executive Officer (“CEO”). You agree to devote your full business time, best efforts, skill, knowledge, attention, and energies to the advancement of the Company’s business and interests and to the performance of your duties
and responsibilities as an employee of the Company, effective on such date as is mutually agreed upon by you and the Company (which shall in no event be later than July 10, 2017). Notwithstanding the foregoing, you may continue to serve as a
member of the Board of Directors of Puma Technologies, Inc. provided that such service does not interfere in any material respect with the performance of your duties for the Company and does not create a conflict of interest. 

Base Salary: Your base salary will be at the rate of $15,000.00 per bi-weekly pay period (which if annualized
equals $390,000), less all applicable taxes and withholdings and which will be paid in accordance with the Company’s regular payroll practices.

Annual Discretionary Bonus: Following the end of each fiscal year, and provided that the Board of Directors of the Company (the “Board”)
approves funding an annual bonus pool for such fiscal year, you will be eligible for a retention and performance bonus (the “Performance Bonus”). The target amount of such Performance Bonus will be 35% of your annualized base salary for
the applicable fiscal year, based on the Company’s achievement of its performance goals and your achievement of your performance goals for the fiscal year. The Board or its designee, in its sole discretion, shall determine whether goals have
been achieved and whether a Performance Bonus will be awarded. Any Performance Bonus will be paid to you following the close of the fiscal year to which it relates (but in no event later than March
15th). In any event, you must be an active employee of the Company on the date any Performance Bonus is distributed in order to be eligible for and to earn a bonus award, as it also








 
serves as an incentive to remain employed by the Company. Any Performance Bonus for the 2017 fiscal year will be pro-rated such that you would receive two-thirds (2/3) of the Performance Bonus you would have received for the year had you been employed during the entirety of such year. 

Sign on Bonus: You will receive a one-time sign-on bonus in the amount
of $50,000.00, less all applicable taxes and withholdings, to be paid on the Company’s first regular pay date whose cutoff date follows your commencement of employment. Please note that if, prior to the
one-year anniversary of your start date, you resign your employment without Good Reason (as defined below) or your employment is terminated for Cause (as defined below), you will be required to repay the
Company (within thirty (30) days following your separation date) an amount equal to $4,166.66 per complete calendar month remaining between your separation date and the one-year anniversary of your start
date. 
 Special Bonus: You will also be eligible to receive a one-time special retention bonus of
$50,000.00, less all applicable taxes and withholdings (the “Special Bonus”), if the Company has [**]. In such event, you will be paid the Special Bonus in the Company’s next regular payroll cycle beginning after such Initiation. You
must be an active employee of the Company on the date any Special Bonus is distributed in order to be eligible for and to earn such bonus. 

Withholdings: All compensation payable to you shall be subject to applicable taxes and withholdings. 

Initial Stock Option Grant: Subject to approval by the Board, you will be granted an option to purchase up to 1,600,000
shares of the Company’s common stock (the “Initial Option”), at a price equal to the fair market value of the common stock on the date of the grant, as determined by the Board. This Initial Option, if granted, will be subject
to the standard terms and conditions of the Constellation Pharmaceuticals Stock Option Plan and the stock option agreement provided in connection therewith. As set forth in the stock option agreement, the Initial Option will vest over four
years at the rate of 25% after twelve months of active employment beginning with start date and an additional 6.25% per quarter in accordance with the specific terms provided in the stock option agreement. 

Performance Stock Option Grant: You will be eligible to receive a performance-accelerated option (the “Performance Grant”) to purchase up to
an additional 800,000 shares of the Company’s common stock, subject to cliff vesting of 100% on the sixth anniversary of your start date, assuming you remain employed by the Company on such anniversary. Tranches of the Performance Grant can
vest earlier than the sixth anniversary, based on satisfying certain performance milestones (and your remaining employed through such satisfaction): 
 [**]

 If and when a performance milestone described above is met (provided that you are then employed by the Company), the number of shares associated with
that milestone will convert to time vesting from your start date at a rate of 6.25% per quarter in accordance with the specific terms provided in the stock option agreement, with any remaining portions of the Performance Grant continuing to be
subject to the six year cliff. The Performance Grant will be subject to approval by the Board and granted at a price equal to the fair market value of the common stock on the date of the grant, as determined by the Board. The Performance Grant will
be subject to the standard terms and conditions of the Constellation Pharmaceuticals Stock Option Plan and the stock option agreement provided in connection therewith. The numbers of shares stated above for the tranches will be adjusted in the same
manner as your Initial Option if the Company’s capitalization changes before the dates of grant (such as in a stock split). 







 Benefits: You may participate in any and all benefit programs that the Company establishes and makes
available to its employees from time to time, provided that you are eligible under (and subject to all provisions of) the plan documents governing those programs, including the Company’s 401(k) plan, which is currently being offered through
Fidelity Investments. Enclosed is a summary of the benefits that are currently provided to the employees of Constellation Pharmaceuticals. Please note that the benefits made available by the Company, and the rules, terms, and conditions for
participation in such benefit plans, may be changed by the Company at any time, and from time to time without advance notice. 
 Change In
Control: The Company has adopted a Change in Control Severance Plan (the “Plan”), in which you are eligible to participate and that will be provided to you under separate cover. The Plan is the sole agreement between the Company and
you governing any compensation and/or benefits, equity or otherwise, that you may be eligible to receive if your employment with the Company (or its successor in a “Change in Control” (as defined in the Plan) is terminated other than for
“Cause” (as defined in the Plan) or terminates for “Good Reason” (as defined in the Plan) during the Protected Period (as defined in the Plan), but not in the event of death or disability. In the event there is a conflict between
the terms of this offer letter and the terms of the Plan, the terms of the Plan shall govern. For the avoidance of doubt, if you are eligible for benefits under the Plan, you will not be eligible to receive the Severance Benefits (as defined below)
or the Additional Severance Benefit (as defined below). The vesting under the Plan will apply to both the Initial Option and the Performance Grant. 

Employment At-Will: This offer letter is not intended to create or constitute an employment agreement or
contract between you and Constellation for any definite period of time and shall not be construed as an agreement, either express or implied, to employ you for any stated term. If you accept the Company’s offer of employment, your
employment with the Company will be on an “at-will” basis, meaning that both the Company and you remain free to end the employment relationship for any reason, at any time, with or without cause or
notice. Although your job duties, title, compensation and benefits, as well as the Company’s personnel policies and procedures, may change from time to time, the “at-will” nature of your
employment may only be changed by a written agreement signed by you and the CEO that expressly states the intention to modify the at-will nature of your employment. Similarly, nothing in this letter shall be
construed as an agreement, either express or implied, to pay you any compensation or grant you any benefit beyond the end of your employment with the Company, except as otherwise explicitly set forth herein. 

Severance Benefits Not in Connection With a Change in Control:

Without limiting the at-will nature of your employment with the Company, in the event that, outside of the Protected
Period (as defined in the Plan), Constellation terminates your employment without Cause (as defined below) or you resign your employment for Good Reason (as defined below), and subject to the Severance Conditions set forth below, Constellation
shall: (i) pay you in one lump sum a severance payment equivalent to (x) twelve (12) months of your then current base salary which amount shall, if your separation occurs prior to the one-year
anniversary of your start date, be multiplied by (y) a fraction the numerator of which is the number of days from the start date through and including the date employment ends and the denominator of which is 365, less all applicable








 
taxes and withholdings (the “Severance Pay”); and (ii) if you are eligible for and timely elect to continue receiving group medical and/or dental insurance under COBRA, until the
earlier of (x) the date that is twelve (12) months following your separation date, and (y) the date on which you obtain alternative coverage (as applicable, the “COBRA Contribution Period”), continue to pay the share of the
premiums for such coverage to the same extent it was paying such premiums on your behalf immediately prior to your separation date (though if, as a result of a change in legal requirements, the Company’s provision of payments for COBRA will
violate the nondiscrimination requirements of applicable law, this COBRA benefit will not apply) (collectively, the “Severance Benefits”). In addition, if (a) a new CEO commences employment with the Company prior to the one-year anniversary of your start date, and (b) the Company terminates your employment without Cause prior to the one-year anniversary of your start date and
(c) the date of such termination occurs outside of the Protected Period (as defined in the Plan), then, subject to the Severance Conditions, instead (and in lieu) of the prorated Severance Pay set forth in clause (i) above, you will
receive a lump sum severance payment equal to twelve (12) months of your then current base salary, and the Initial Option shall vest and become immediately exercisable based on 2.0833% of the number of shares under the Initial Option times the
number of full calendar months elapsed since the start date as of the date of termination (together, the “Additional Severance Benefit”) and any remaining portions of the Initial Option will immediately expire. 

The Company’s obligation to provide you with the Severance Benefits and/or the Additional Severance Benefit is contingent upon your entering into a
Severance and Release of Claims Agreement (the “Severance Agreement”) in a form to be provided by the Company (which will include, at a minimum, a release of all releasable claims you may have and your agreement to non-disparagement, confidentiality, and cooperation obligations). The Severance Agreement must be signed by you, and any applicable revocation period with respect thereto must have expired, by the 60th day following the end of your employment (or such shorter period as the Company may specify). Payment of the Severance Pay will be made on the first regular payday after the Severance Agreement
becomes effective; provided, however, that if the 60th day following your separation date occurs in the calendar year following the year of your separation, then payment shall not be made
before January 1 of such subsequent calendar year. 
 Cause: For purposes of this offer letter, “Cause” shall mean (i) a material
breach of any material term of any applicable offer letter or agreement between you and the Company, including the Employee Non-Competition, Non-Solicitation,
Confidentiality and Assignment Agreement referred to below, (ii) your plea of guilty or nolo contendere to, or your conviction of, a felony offense or a crime of dishonesty, (iii) your repeated unexplained or unjustified absences, refusals
or failures to carry out the lawful directions of the Board or the CEO, or (iv) your willful misconduct that results or is reasonably likely to result in material harm to the Company. 

Good Reason: For purposes of this offer letter, “Good Reason” shall mean (i) a material reduction of your base salary, (ii) a
material diminution of your authority, duties, or responsibilities, (iii) a requirement that your principal place of providing services to the Company change by more than 50 miles, other than in a direction that reduces your daily commuting
distance; or (iv) any material breach by the Company of a material provision of any agreement between you and the Company under which you provide services. Notwithstanding the occurrence of any of the foregoing events or circumstances, a
resignation shall not be deemed to constitute resignation for Good Reason unless (x) you give the Company a written notice of the purported Good Reason (no more than 90 days after the initial 







 
existence of such event or circumstance), (y) such event or circumstance has not been fully corrected (and you have not been reasonably compensated for any losses or damages resulting therefrom)
within 30 days following the Company’s receipt of such notice, and (z) if the Company does not correct, you end your employment not more than 30 days following the period to correct in (y). 

Payments Subject to Section 409A: This offer letter, and any payments or other benefits under this offer letter, is intended to
comply, to the extent applicable, with the provisions of Section 409A of the Internal Revenue Code of 1986, as amended (“Section 409A”) and shall, to the extent practicable, be construed in accordance with such section and consistent
with Exhibit A to this offer letter. 
 Employment Eligibility: This offer of employment is contingent upon satisfactory reference
checks, your signing Constellation’s standard form of Employee Non-Competition, Non-Solicitation, Confidentiality and Assignment Agreement (the “Non-Compete”), a copy of which is enclosed, and I-9 Employment Verification. You will be required to submit documentation that establishes your identity and
employment eligibility in accordance with the US Immigration and Naturalization requirements within the first three days of your employment with the Company.

Company Policies and Procedures: As an employee of the Company, you will be required to comply with all Company policies and procedures. Violations of
the Company’s policies may lead to immediate termination of your employment. Further, the Company’s premises, including all workspaces, furniture, documents, and other tangible materials, and all information technology resources of the
Company (including computers, data and other electronic files, and all internet and email) are subject to oversight and inspection by the Company at any time. Company employees should have no expectation of privacy with regard to any Company
premises, materials, resources, or information. 
 Miscellaneous: You represent that you are not bound by any employment contract, restrictive
covenant or other restriction preventing you from entering into employment with or carrying out your responsibilities for the Company, or which is in any way inconsistent with the terms of this letter. If there are any agreements of any type that
you are aware of which may impact or limit your ability to perform your job at the Company, please let us know as soon as possible. 

Please note that this offer letter is your formal offer of employment and supersedes any and all prior or contemporaneous agreements,
discussions and understandings, whether written or oral, relating to the subject matter of this letter or your employment with the Company. The resolution of any disputes under this letter will be governed by Massachusetts law. 

Please indicate your acceptance of this offer by signing in the appropriate space below and returning a signed copy of this offer letter along
with a signed copy of the Non-Compete to the attention of Brenda Sousa at Constellation Pharmaceuticals. We will discuss a formal start date and transition plan upon your acceptance of this offer. 

We are all very excited about the opportunity to work with you, Adrian. Feel free to contact Brenda Sousa or me if you have any questions or
need more information. On behalf of all our team members, let me extend a sincere welcome. 
 Sincerely, 








	
	/s/ Jigar Raythatha
	Jigar Raythatha
	President & CEO
	Constellation Pharmaceuticals, Inc.

 The foregoing correctly sets forth the terms of my at-will employment with
Constellation Pharmaceuticals, Inc. I am not relying on any representations other than those set forth above. 
  

							
	/s/ Adrian Senderowicz	 		 	7/6/17	 	  

	Adrian Senderowicz, MD	 		 	Date	 	

 Enclosures: 
 ~Summary of
Constellation Benefits 
 ~Constellation’s Employee Non-Competition,
Non-Solicitation, Confidentiality and Assignment Agreement 







 Exhibit A 

Payments Subject to Section 409A 
 The
following rules shall apply with respect to distribution of the payments and benefits, if any, to be provided under this offer letter: 
  

	 	(a)	It is intended that each installment of the severance payments and benefits provided under this offer letter shall be treated as a separate “payment” for purposes of Section 409A of the Internal Revenue
Code and the guidance issued thereunder (“Section 409A”). Neither you nor Constellation shall have the right to accelerate or defer the delivery of any such payments or benefits except to the extent specifically permitted or required
by Section 409A. 

  

	 	(b)	If, as of the date of your “separation from service” from Constellation, you are not a “specified employee” (within the meaning of Section 409A), then each installment of the severance payments
and benefits shall be made on the dates and terms set forth in this offer letter. 

  

	 	(c)	If, as of the date of your “separation from service” from Constellation, you are a “specified employee” (within the meaning of Section 409A), then: 


 

	 	(i)	Each installment of the severance payments and benefits due under this offer letter that is paid within the short-term deferral period (as defined under Section 409A) shall be treated as a short-term deferral
within the meaning of Treasury Regulation Section 1.409A-1(b)(4) to the maximum extent permissible under Section 409A and shall be made on the dates and terms set forth in this offer letter; and


  

	 	(ii)	Each installment of the severance and benefits due under this offer letter that is not described in paragraph (i) above and that would, absent this subsection, be paid within the
six-month period following your “separation from service” from Constellation shall not be paid until the date that is six months and one day after such separation from service, (or, if earlier, upon
your death), with any such installments that are required to be delayed being accumulated during the six-month period and paid in a lump sum on the date that is six months and one day following your separation
from service and any subsequent installments, if any, being paid in accordance with the dates and terms set forth herein; provided, however, that the preceding provisions of this sentence shall not apply to any installment of severance payments and
benefits if any to the maximum extent that such installment is deemed to be paid under a separation pay plan that does not provide for a deferral of compensation by reason of the application of Treasury Regulation
Section 1.409A-1(b)(iii) (relating to separation pay upon an involuntary “separation from service”. Any installments that qualify for the exception under Treasury Regulation Section 1.409A-1(b)(9)(iii) must be paid no later than the last day of your second taxable year following the taxable year in which separation from service occurs. 









	 	(d)	The determination of whether and when your separation from service from Constellation has occurred shall be made and in a manner consistent with, and based on the presumptions set forth in, Treasury Regulation Section 1.409A-1(h). Solely for purposes of this paragraph (d), “Constellation” shall include all persons with whom Constellation would be considered a single employer under Sections 414(b) and 414(c)
of the Code. 

  

	 	(e)	All reimbursements and in-kind benefits provided under this offer letter shall be made or provided in accordance with the requirements of Section 409A to the extent that such
reimbursements or in-kind benefits are subject to Section 409A, including, where applicable the requirement that (i) any reimbursement is for expenses incurred during your lifetime (or during a
shorter period of time specified in this offer letter), (ii) the amount of expenses eligible for reimbursement during a calendar year may not affect the expenses eligible for reimbursement in any other calendar year, (iii) the reimbursement of
an eligible expense will be made on or before the last day of the calendar year following the year in which the expense is incurred and (iv) the right to reimbursement is not subject to set off or liquidation or exchange for any other benefit.


  

	 	(f)	Notwithstanding anything to the contrary in this offer letter, any payment or benefit under this offer letter or otherwise that may be exempt from Section 409A pursuant to Treasury Regulation Section 1.409A-1(b)(9)(v)(A) or (C) (relating to certain reimbursements and in-kind benefits) shall be paid or provided to you only to the extent that the expenses are
not incurred, or the benefits are not provided, beyond the last day of the second calendar year following the calendar year in which your “separation from service” occurs; and provided further that such expenses are reimbursed no later
than the last day of the third calendar year following the calendar year in which your “separation from service” occurs.