Exhibit 10.6.1  125
Hartwell Avenue Lexington,
Massachusetts 02421 (the
Building)  SEVENTH
AMENDMENT November 26, 2007   LANDLORD:
  
  125
  Hartwell Trust, under a declaration of trust dated February 20, 1980 and
  filed with the Middlesex South Registry District of the Land Court as
  Document No. 600788, as amendedTENANT:
  
  Synta
  Pharmaceuticals Corp., a Delaware corporation, successor-by-assignment to EMD
  Pharmaceuticals, Inc.PREMISES:
  
  Collectively,
  (i) approximately 19,810 square feet of Premises Rentable Area on the
  second (2nd) floor of the Building, consisting of approximately 10,980square feet of Premises
  Rentable Area under theoriginal Lease shown as
  the Premises on
  Exhibit 3
  thereto, plus approximately 8,830 square feet of Premises Rentable Area added
  by the First Amendment referred to below shown as the RFO Premises on said
  Exhibit 3, and (ii) approximately 2,670 square feet of Premises
  Rentable Area on the first (1st) floor of the Building,
  substantially as shown cross-hatched on Exhibit A attached to the Fifth
  Amendment referred to belowEXISTING
  LEASE
  DATALEASEEXECUTIONDATE:
  
  October 26,
  1992TERMINATIONDATE:
  
  January 31,
  2008PREVIOUSLEASEAMENDMENTS:
  
  First
  Amendment dated as of January 31, 1993
  Second
  Amendment dated October 1, 1997Third
  Amendment dated November 1, 2002
  Assignment
  and Assumption of Lease and Consent of and Release by Landlord and Fourth
  Amendment to Lease dated as of July 9, 2004 (the Assignment/Fourth
  Amendment)
  Fifth
  Amendment dated October 22, 2004
  Sixth
  Amendment dated August 1, 2005   1


WHEREAS, Tenant, by notice to
Landlord dated April 30, 2007, has exercised its option to extend the Term
of the above-described lease, as previously amended (the Lease), for the
first of the three (3) successive additional terms provided in Paragraph 1
of the Sixth Amendment to the Lease; and  WHEREAS, Landlord and Tenant
desire to confirm the terms and conditions applicable to the demise of the
Premises for such additional term.  NOW THEREFORE, the parties
hereby agree that the Lease is hereby amended by this Seventh Amendment (this Amendment)
as follows (capitalized terms used herein without definition shall have the
meanings ascribed to them in the Lease):  1.             EXTENSION OF TERM  The
Term of the Lease is hereby extended for an additional term commencing as of February 1,
2008 and expiring as of November 30, 2011. 
The demise of the Premises for such additional term shall be upon and
governed by the terms and conditions of the Lease (as hereby amended) in effect
immediately prior to the commencement of such additional term, except as
follows or as otherwise provided in this Amendment:  A.            The Basic Rent payable by Tenant during such additional
term shall be the sum of (x) the Basic Rent payable by Tenant in respect
of the Premises as of January 31, 2008, plus (y) the aggregate
amounts payable by Tenant under the Lease on account of Building Expenses
(i.e., the Building Expense Escalation Charge) in respect of calendar years
2005, 2006 and 2007, less the portion(s), if any, of any such amounts that have
been previously included in the Basic Rent set forth in the foregoing clause (x) [by
way of clarification, and notwithstanding anything to the contrary contained in
the Lease, the aggregate Building Expense Escalation Charges payable in respect
of each calendar year (once finally determined) are included in the Basic Rent
payable for the subsequent calendar year and the Building Expense Base, for
purposes of determining the Building Expense Escalation Charges payable in
respect of such subsequent calendar year, is changed to the prior calendar years
Building Expenses].  B.            The Building Expense Base in respect of such additional
term shall be the amount of Building Expenses for calendar year 2007
(accordingly, Tenants obligation to pay Building Expense Escalation Charges in
respect of such additional term shall commence to accrue as of February 1,
2008).  C.            There shall be no Building Expense Cap during or in
respect of such additional term.  D.            Tenant shall have the right to continue to use the
Included Property and the Assignors Improvements (as defined in Paragraphs 11
and 12, respectively, of the    2


Assignment/Fourth
Amendment) during such additional term in accordance with and subject to the
terms and provisions of Paragraphs 11 and 12 of the Assignment/Fourth
Amendment, except that (even if Tenant shall use such Included Property and
Assignors Improvements) Tenant shall have no obligation to pay the Monthly
Improvements Rent in respect of such additional term.  E.             Landlord shall have no obligation to reconstruct or
renovate the Premises for Tenants occupancy during such additional term or to
provide any allowance or contribution with respect thereto.  2.             BROKER  Each party (the indemnifying
party) represents and warrants to the other party that it has not dealt with
any broker or agent in connection with this Amendment.  The indemnifying party shall indemnify and
hold the other party (and such other partys trustees, beneficiaries, agents
and employees) harmless of and from all claims that may be made by any person
against such other party (or its trustees, beneficiaries, agents or employees)
for brokerage or other compensation in the nature of brokerage with respect to
this Amendment on account or arising out of the indemnifying partys dealings
with such person.  Landlord shall pay the
commission owed to Richards Barry Joyce & Partners in connection with
this Amendment pursuant to a separate agreement between Landlord and such
party.  3.             MISCELLANEOUS  As amended by this Amendment,
the Lease is hereby ratified, approved and confirmed in all respects and
Landlord and Tenant each hereby acknowledge and confirm that, to the best of
its respective knowledge, neither the Landlord nor the Tenant is in default
of any term or condition of the Lease. 
In the event of a conflict between the Lease and this Amendment, the
terms of this Amendment shall govern.  WHEREFORE, the parties have
hereunto set their hands and seals as of the date first above written.  LANDLORD:
  TENANT:SYNTA
  PHARMACEUTICALS CORP./s/
  STEVEN COLANGELO
  
  By:
  /s/
  KEITH EHRLICHSteven
  Colangelo, signing as
  
  Name:
  Keith
  EhrlichTrustee
  of 125 Hartwell Trust and not
  
  Title:
  CFOindividually
  and without recourse
  
  Hereunto
  Duly Authorizedagainst
  the Trustee personally or hisassets   3