Document:

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.EX-10.22

 Exhibit 10.22 

Constellation Pharmaceuticals, Inc. 

Change in Control Severance Plan 

September 23, 2010 

1. Establishment of Plan. Constellation Pharmaceuticals, Inc. (the “Company” or
“Constellation”) hereby establishes an unfunded severance benefits plan (the “Plan”) that is intended to be a welfare benefit plan within the meaning of Section 3(1) of the Employee Retirement
Income Security Act of 1974, as amended (“ERISA”). The Plan is in effect for covered employees whose employment is terminated involuntarily in connection with a Change in Control (defined below) occurring after
September 1, 2010 (the “Effective Date”) and before the termination of this Plan. This Plan supersedes any and all severance plans or separation policies applying to covered employees that may have been in
effect before the effective date of this Plan throughout the Company with respect to any termination of employment during the Protected Period (as defined below). However, it is not intended to supersede, but may supplement, individual written
agreements that provide for severance in lieu of benefits under general severance policies or plans. 
 2. Purpose. The purpose
of the Plan is to establish the conditions under which covered employees (defined below) will receive severance benefits described herein if employment with the Company (or its successor in a Change in Control) is terminated other than for
“Cause” during the Protected Period. The severance benefits paid under the Plan are intended to assist employees in making a transition to new employment and are not intended to be a reward for prior service with the Company. 

3. Coverage. Covered employees may be entitled to receive the severance benefits under the Plan if they are terminated
without “Cause” (defined below) within the period beginning with the date of a letter of intent or similar agreement that does lead to a Change in Control through the one-year anniversary of the
Change in Control event (the “Protected Period”). In addition, in order to receive the severance benefits under the Plan, covered employees must meet the eligibility and other requirements provided below in Sections 5 and 6
of the Plan. A covered employee who is a Company officer, holding the title of vice president or above (“Officer”), is also eligible to receive severance benefits under the Plan if such Officer terminates his employment for
“Good Reason” (defined below) during the Protected Period. 
 A. Covered employees are all regular full-time and
regular part-time employees (both exempt and non-exempt) whose employment with the Company is terminated without Cause (or for Officers, without Cause or for Good Reason) during the Protected Period
(“covered employees” or “participants”) and who are designated as eligible to receive severance benefits under the Plan as provided in Section 5. Temporary employees are not eligible for severance
benefits under the Plan. 
 B. For the purpose of this Plan, “regular full-time employees” are
employees, other than temporary employees, normally scheduled to work at least 40 hours a week unless the Company’s local practices, as from time to time in force, whether or not in writing, establish a different hours threshold for regular
full-time 

 
employees. “Regular part-time employees” are employees, other than temporary employees, treated as such by the Company, whether or not in writing. Regular part-time
employees will be considered covered employees for purposes of the Plan. “Temporary employees” are employees treated as such by the Company, whether or not in writing. An employee’s part-time, full-time or temporary
status for the purpose of this Plan is determined by the Company upon review of the employee’s status immediately before termination. 

C. Any person who is classified by the Company as an independent contractor or third party employee is not eligible for
severance benefits even if such classification is modified retroactively. 
 4. Definitions. For purposes of this
Plan, 
 A. “Change in Control” shall mean the occurrence of any of the following events, provided
that such event or occurrence constitutes a change in the ownership or effective control of Constellation, or a change in the ownership of a substantial portion of the assets of Constellation, as defined in Treasury Regulation §§1.409A-3(i)(5)(v), (vi) and (vii): (i) any merger or consolidation that results in the voting securities of Constellation outstanding immediately prior thereto representing (either by remaining
outstanding or by being converted into voting securities of the surviving or acquiring entity) less than 50% of the combined voting power of the voting securities of Constellation or such surviving or acquiring entity outstanding immediately after
such merger or consolidation; (ii) any sale of all or substantially all of the assets of Constellation; (iii) the complete liquidation or dissolution of Constellation; or (iv) the acquisition of “beneficial ownership” (as
defined in Rule 13d-3 under the Exchange Act) of securities of Constellation representing 50% or more of the combined voting power of Constellation’s then outstanding securities (other than through a
merger or consolidation or an acquisition of securities directly from Constellation) by any “person,” as such term is used in Sections 13(d) and 14(d) of the Exchange Act, other than Constellation, any trustee or other fiduciary holding
securities under an employee benefits plan of Constellation or any corporation owned directly or indirectly by the stockholders of Constellation in substantially the same proportion as their ownership of stock of Constellation. 

B. “Cause” shall mean (i) a material breach of any material term of any applicable offer letter or
the Employee Non-Competition, Non-Solicitation, Confidentiality and Assignment Agreement referred to below, (ii) a plea of guilty or nolo contendere to, or
conviction of, the commission of a felony offense or a crime of dishonesty, (iii) repeated unexplained or unjustified absences, refusals or failures to carry out the lawful directions of the Board of Directors of the Company (the
“Board”) or the Chief Executive Officer, or the employee’s supervisor, or (iv) willful misconduct that results or is reasonably likely to result in material harm to Constellation. 

  
 2 

 C. “Good Reason” is defined as: (1) a material
diminution in the Officer’s base compensation; (2) a material diminution in the Officer’s authority, duties, or responsibilities; (3) a material diminution in the authority, duties, or responsibilities of the employee to whom the
Officer is required to report, including a requirement that an Officer report to a corporate officer or employee instead of reporting directly to the Board (or similar governing body with respect to an entity other than a corporation); (4) a
material diminution in the budget over which the Officer retains authority; (5) a material change in the geographic location at which the Officer must perform the services; or (6) any other action or inaction that constitutes a material
breach by the Company of any agreement under which the Officer provides services. 
 In order to establish a “Good Reason” for
terminating employment, an Officer must provide written notice to the Company of the existence of the condition giving rise to the Good Reason, which notice must be provided within 90 days of the initial existence of such condition, the Company must
fail to cure the condition within 30 days thereafter, and an Officer’s termination of employment must occur no later than one year following the initial existence of the condition giving rise to Good Reason. 

5. Eligibility for Severance Benefits. To receive severance benefits under the Plan, a covered employee must be specifically
identified by the Company as eligible to receive severance benefits. The following covered employees will generally not be eligible for severance benefits: (1) an employee who is terminated for Cause; (2) an employee who retires,
terminates employment as a result of an inability to performs his duties due to physical or mental disability or dies; (3) an employee who voluntarily terminates his employment, except a termination for Good Reason as specified above by an
Officer; (4) an employee who is employed for a specific period of time in accordance with the terms of a written employment agreement; (5) an employee who promptly becomes employed by another member of the controlled group of entities of which
Constellation (or its successor in the Change in Control) is a member as defined in Sections 414(b) and (c) of the Internal Revenue Code of 1986, as amended (“Code”); and (6) an employee who loses employment in
connection with a Change in Control event, outsourcing arrangement or other corporate transaction and who accepts employment with an acquirer of any of the businesses, operations or assets of the Company or refuses an offer of such employment in a
position providing comparable responsibilities and compensation. 
 6. Severance Benefits. Receipt of any
severance benefits under the Plan requires that the participant (1) comply with the provisions of any applicable noncompetition, nonsolicitation, and other obligations to the Company, and (2) execute and deliver a suitable waiver and
release under which the participant releases and discharges the Company and its affiliates from and on account of any and all claims that relate to or arise out of the employment relationship between the Company and the participant (“the
Release) which Release becomes binding within 60 days following the participant’s termination of employment. The “Severance Pay” (as defined below) will be paid in a lump sum and the “Benefits
Continuation” (as defined below) will be paid in the amount and at the time such premium payments are made by other participants in the Company’s health benefit plans with the same coverage. The payments shall be made or commence within 10
business days after the Release becomes irrevocable. 

  
 3 

 The covered employee’s unvested equity grants (as described under “Equity
Acceleration” below), shall immediately vest or the substantial risk of forfeiture shall lapse, as applicable, upon the covered employee’s termination from employment that gives rise to severance benefits under this Plan; provided that
(x) the employee may not exercise or dispose of any such otherwise unvested portions of the equity grants until the Release has become binding ( as provided above) and (y) provided further that, if the Release does not become binding
within such 60 days the portion of the employee’s equity grants that became vested or with respect to which the substantial risk of forfeiture lapsed pursuant to the earlier part of this sentence shall expire or be forfeited, as applicable, as
of the date of termination from employment. 
 7. Cash Severance. The cash portion of the severance benefits to be paid
(“Severance Pay”) will equal: (1) payment of a pro rata portion of the participant’s target bonus that has been established for the year of termination (or is established thereafter, basing the target bonus for such
participant on the position held by the participant prior to employment termination), if any; and (2) the amount of the participant’s monthly base salary multiplied by the “Severance Period,” as provided in the table below. In
calculating the Severance Pay, the “base salary” shall be the base rate of pay as in effect immediately before termination (or prior to the Change of Control, if greater) and exclusive of any bonuses, overtime pay, shift differentials,
“adders,” any other form of premium pay, or other forms of compensation. 
  

			
	 Job title of participant
	  	 Severance Period

	Chief Executive Officer	  	18 months
		
	Vice President and above	  	12 months
		
	Directors up to but not including Vice Presidents	  	6 months
		
	All other participants	  	3 months plus one week for every “Year of Service” (as defined below)

 The covered employee’s years of service (“Years of Service”) with the Company are calculated by
dividing the total number of days between and including an employee’s hire date and termination date by 365 and taking that number to the second decimal point. If the covered employee has been rehired after a break in continuous service, the
employee’s Years of Service are calculated from the most recent hire date. 

  
 4 

 8. Other Severance Benefits. In addition to the forgoing Severance Pay, the
severance benefits under the Plan shall include the following benefits: 
 A. Company contributions to the cost of COBRA
(Consolidated Omnibus Budget Reconciliation Act) coverage on behalf of the participant and any applicable dependents for no longer than the Severance Period if the participant elects COBRA coverage, and only so long as such coverage continues in
force. Such costs shall be determined on the same basis as the Company’s contribution to Company-provided health and dental insurance coverage in effect immediately before the participant’s termination for an active employee with the same
coverage elections; provided that if the participant commences new employment and is eligible for a new group health plan, the Company’s continued contributions toward health and dental coverage shall end when the new employment begins
(“Benefits Continuation”); and 
 B. Full vesting of all of the participant’s unvested equity
grants (“Equity Acceleration”). 
 C. The amount of any bonus for the prior year that was approved
but not yet paid to the participant at the time of the participant’s termination of employment, or, if not yet approved, then the amount that is approved subsequent to such termination (determined without regard to the participant’s
termination of employment), paid in a manner and timing consistent with the payments to other similarly situated employees and consistent with the requirements of Section 409A of the Code. 

9. Recoupment. If a participant fails to comply with the terms of the Plan, including the provisions of Section 6 above, the
Company may require payment to the Company of any Severance Pay, Benefits Continuation or value upon vesting of unvested equity grants under the provision for Equity Acceleration that the participant has already received to the extent permitted by
applicable law and with the “value” determined in the sole discretion of the Plan Administrator. Payment is due in cash or by check within 10 days after the Company provides notice to a participant that it is enforcing this provision. Any
Severance Pay, Benefits Continuation or Equity Acceleration not yet received will also be immediately forfeited. 
 10.
Withholding. The Company may withhold from any payment or benefit under the Plan: (1) any federal, state, or local income or payroll taxes required by law to be withheld with respect to such payment; (2) such sum as the Company may
reasonably estimate is necessary to cover any taxes for which the Company may be liable and which may be assessed with regard to such payment; and (3) such other amounts as appropriately may be withheld under the Company’s payroll policies
and procedures from time to time in effect. 
 11. Section 409A. It is expected that the payments and benefits provided under
this Plan will be exempt from the application of Section 409A of the Code, and the guidance issued thereunder (“Section 409A”). The Plan shall be interpreted consistent with this intent
to the maximum extent permitted and generally, with the provisions of Section 409A. A termination of employment shall not be deemed to have occurred for purposes of any provision of this Plan providing for the payment of any amounts or benefits
upon or following a termination of employment unless such termination is also a “separation from service” within the meaning of Section 409A and, for purposes of any such provision of this Plan, references to a
“termination,” “termination of employment” or like terms shall mean “separation from service”. Neither the participant nor the Company shall have the right to accelerate or defer the delivery of any payment or benefit
except to the extent specifically permitted or required by Section 409A. 

  
 5 

 Notwithstanding the following, to the extent the severance benefits under this Plan are subject
to Section 409A, the following rules shall apply with respect to distribution of the payments and benefits, if any, to be provided to participants under this Plan: 

A. Each installment of the payments and benefits provided under this Plan will be treated as a separate “payment” for
purposes of Section 409A. Whenever a payment under this Plan specifies a payment period with reference to a number of days (e.g., “payment shall be made within 10 days following the date of termination”), the actual date of
payment within the specified period shall be in the Company’s sole discretion. Notwithstanding any other provision of this Plan to the contrary, in no event shall any payment under this Plan that constitutes
“non-qualified deferred compensation” for purposes of Section 409A be subject to offset, counterclaim or recoupment by any other amount unless otherwise permitted by Section 409A. 

B. Notwithstanding any other payment provision herein to the contrary, if the Company or appropriately-related affiliates
become publicly-traded and a covered employee is deemed on the date of termination to be a “specified employee” within the meaning of that term under Code Section 409A(a)(2)(B) with respect to such entity, then each of the following
shall apply: 
 (i) With regard to any payment that is considered “non-qualified
deferred compensation” under Section 409A payable on account of a “separation from service,” such payment shall be made on the date which is the earlier of (A) the day following the expiration of the six month period
measured from the date of such “separation from service” of the covered employee, and (B) the date of the covered employee death (the “Delay Period”) to the extent required under Section 409A. Upon the expiration
of the Delay Period, all payments delayed pursuant to this provision (whether otherwise payable in a single sum or in installments in the absence of such delay) shall be paid to or for the covered employee in a lump sum, and all remaining payments
due under this Plan shall be paid or provided for in accordance with the normal payment dates specified herein; and 
 (ii)
To the extent that any benefits to be provided during the Delay Period are considered “non-qualified deferred compensation” under Section 409A payable on account of a “separation from
service,” and such benefits are not otherwise exempt from Section 409A, the covered employee shall pay the cost of such benefits during the Delay Period, and the Company shall reimburse the covered employee, to the extent that such costs
would otherwise have been paid by the Company or to the extent that such benefits would otherwise have been provided by the Company at no cost to the covered employee, the Company’s share of the cost of such benefits upon expiration of the
Delay Period. Any remaining benefits shall be reimbursed or provided by the Company in accordance with the procedures specified in this Agreement. 

  
 6 

 C. To the extent that severance benefits pursuant to this Plan are conditioned
upon a Release, the covered employee shall forfeit all rights to such payments and benefits unless such release is signed and delivered (and no longer subject to revocation, if applicable) within 60 days following the date of the termination of the
covered employee’s employment with the Company. If the Release is no longer subject to revocation as provided in the preceding sentence, then the following shall apply: 

(i) To the extent any severance benefits to be provided are not “non- qualified
deferred compensation” for purposes of Section 409A, then such benefits shall commence upon the first scheduled payment date immediately after the date the Release is executed and no longer subject to revocation (the “Release
Effective Date”). The first such cash payment shall include all amounts that otherwise would have been due prior thereto under the terms of this Agreement applied as though such payments commenced immediately upon the termination of covered
employee’s employment with the Company, and any payments made after the Release Effective Date shall continue as provided herein. The delayed benefits shall in any event expire at the time such benefits would have expired had such benefits
commenced immediately following the termination of covered employee’s employment with the Company. 
 (ii) To the extent
any such severance benefits to be provided are “non- qualified deferred compensation” for purposes of Section 409A, then the Release must become irrevocable within 60 days of the date of
termination and benefits shall be made or commence upon the date provided in Section 6, provided that if the 60th day following the termination of Executive’s employment with the Company falls in the calendar year following the calendar
year containing the date of termination, the benefits will be made no earlier than the first business day of that following calendar year. The first such cash payment shall include all amounts that otherwise would have been due prior thereto under
the terms of this Agreement had such payments commenced immediately upon the termination of Executive’s employment with the Company, and any payments made after the first such payment shall continue as provided herein. The delayed benefits
shall in any event expire at the time such benefits would have expired had such benefits commenced immediately following the termination of Executive’s employment with the Company. 

D. The Company makes no representations or warranties and shall have no liability to any participant or any other person, other
than with respect to payments made by the Company in violation of the provisions of this Plan, if any provisions of or payments under this Plan are determined to constitute deferred compensation subject to Section 409A of the Code but not to
satisfy the conditions of that section. 

  
 7 

 12. Plan Administration. 

A. Plan Administrator. The Plan Administrator shall be a Committee appointed by the Company following a Change in
Control, which shall also serve as the Named Fiduciary of the Plan under the Employee Retirement Income Security Act of 1974, as amended (“ERISA”). The Plan Administrator shall be the “administrator” within the meaning of
Section 3(16) of ERISA and shall have all the responsibilities and duties contained therein. 
 The Plan Administrator can be contacted
at the following address: 
 Change in Control Severance Plan Committee 

c/o Constellation Pharmaceuticals, Inc. 

215 First Street, Suite 200 

Cambridge, MA. 02138 

B. Decisions, Powers and Duties. The general administration of the Plan and the responsibility for carrying out its
provisions shall be vested in the Plan Administrator. The Plan Administrator shall have such powers and authority as are necessary to discharge such duties and responsibilities which also include, but are not limited to, interpretation and
construction of the Plan, the determination of all questions of fact, including, without limit, eligibility, participation and benefits, the resolution of any ambiguities and all other related or incidental matters, and such duties and powers of the
plan administration which are not assumed from time to time by any other appropriate entity, individual or institution. The Plan Administrator may adopt rules and regulations of uniform applicability in its interpretation and implementation of the
Plan. 
 The Plan Administrator shall discharge its duties and responsibilities and exercise its powers and authority in its sole discretion
and in accordance with the terms of the controlling legal documents and applicable law, and its actions and decisions that are not arbitrary and capricious shall be binding on any employee, and employee’s spouse or other dependent or
beneficiary and any other interested parties whether or not in being or under a disability. 
 13. Indemnification. To
the extent permitted by law, all employees, officers, directors, agents and representatives of the Company shall be indemnified by the Company and held harmless against any claims and the expenses of defending against such claims, resulting from any
action or conduct relating to the administration of the Plan, whether as a member of the Committee or otherwise, except to the extent that such claims arise from gross negligence, willful neglect, or willful misconduct. 

14. Plan Not an Employment Contract. The Plan is not a contract between the Company and any employee, nor is it a condition of
employment of any employee. Nothing contained in the Plan gives, or is intended to give, any employee the right to be retained in the service of the Company, or to interfere with the right of the Company to discharge or terminate the employment of
any employee at any time and for any reason. No employee shall have the right or claim to benefits beyond those expressly provided in this Plan, if any. All rights and claims are limited as set forth in the Plan. 

  
 8 

 15. Severability. In case any one or more of the provisions of this Plan (or part
thereof) shall be held to be invalid, illegal or unenforceable in any respect, such invalidity, illegality or unenforceability shall not affect the other provisions hereof, and this Plan shall be construed as if such invalid, illegal or
unenforceable provisions (or part thereof) never had been contained herein. 
 16.
Non-Assignability. No right or interest of any covered employee in the Plan shall be assignable or transferable in whole or in part either directly or by operation of law or otherwise, including, but
not limited to, execution, levy, garnishment, attachment, pledge or bankruptcy. 
 17. Integration With Other Pay or Benefits
Requirements. The severance benefits provided for in the Plan are the maximum benefits that the Company will pay to covered employees on a termination of employment following a Change in Control, except to the extent otherwise specifically
provided in a separate agreement. To the extent that the Company owes any amounts in the nature of severance benefits under any other program, policy or plan of the Company that is not otherwise superseded by this Plan, or to the extent that any
federal, state or local law, including, without limitation, so-called “plant closing” laws, requires the Company to give advance notice or make a payment of any kind to an employee because of that
employee’s involuntary termination due to a layoff, reduction in force, plant or facility closing, sale of business, or similar event, the benefits provided under this Plan or the other arrangement shall either be reduced or eliminated to avoid
any duplication of payment. The Company intends for the benefits provided under this Plan to partially or fully satisfy any and all statutory obligations that may arise out of an employee’s involuntary termination for the foregoing reasons and
the Company shall so construe and implement the terms of the Plan. 
 18. Amendment or Termination. The Board may amend,
modify, or terminate the Plan at any time on six months advance notice. Such amendment, modification, or termination shall be effected by a written instrument executed by an authorized officer of the Company. 

19. Governing Law. The Plan and the rights of all persons under the Plan shall be construed in accordance with and under
applicable provisions of ERISA, and the regulations thereunder, and the laws of the Commonwealth of Massachusetts (without regard to conflict of laws provisions) to the extent not preempted by federal law. 

  
 9 

 Amendment No. 1 to 

Change in Control Severance Plan 

This AMENDMENT NO. 1 to the Change in Control Severance Plan dated September 23, 2010 (the “Plan”) of Constellation
Pharmaceuticals, Inc. (the “Company”) is made as of January 5, 2012. Capitalized terms used but not otherwise defined herein shall have the meanings ascribed to such terms in the Plan. 

WHEREAS, the Board of Directors of the Company (the “Board”) designed the Plan to provide separation pay and benefits to
certain eligible employees of the Company whose employment is involuntarily terminated without Cause within the period beginning with the date of a letter of intent or similar agreement that does lead to a Change in Control through the one-year anniversary of the Change in Control event; 
 WHEREAS, the Board wishes to clarify that it did
not, and does not, intend the term “letter of intent or similar agreement” to include agreements in the nature of the Agreement and Plan of Merger (the “Merger Agreement”) to be entered into by and among the Company,
Genentech, Inc. (“Genentech”), Hydra Acquisition Corp. and Robert Tepper M.D., as representative of Third Rock Ventures, as representative of the Participating Equity Holders (as defined in the Merger Agreement), or the Option
Agreement to be entered into between the Company and Genentech, which agreements the Company is proposing to enter into; 
 NOW, THEREFORE,
in consideration for the mutual promises contained herein, the Plan is amended as follows. 
 1. The following clarification to the Plan is
hereby made by adding the following sentence immediately after the first sentence of Section 3 thereof: 
 “For the avoidance of
doubt, neither the Agreement and Plan of Merger by and among the Company, Genentech, Inc. (“Genentech”), Hydra Acquisition Corp. and Robert Tepper M.D., as representative of Third Rock Ventures, as representative of the
Participating Equity Holders (as defined therein), or the Option Agreement between the Company and Genentech (the “Option Agreement”) shall be deemed a letter of intent or similar agreement for purposes of the Plan, provided,
however, that any valid exercise by Genentech of its option to acquire the Company pursuant to the Option Agreement shall be deemed a letter of intent or similar agreement for purposes of the Plan.”

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