Exhibit 10.52  CONFIDENTIAL TREATMENT  SECOND
AMENDMENT TO THE COMMERCIAL
SERVICES AGREEMENT  This Second Amendment to the
Commercial Services Agreement (this Second Amendment)
is made this 20thday of May, 2009 (the Amendment
Effective Date), by and between ASTRAZENECA PHARMACEUTICALS LP, a
Delaware limited partnership (AstraZeneca),
and CUBIST PHARMACEUTICALS, INC., a Delaware corporation (Cubist).  WHEREAS, AstraZeneca and
Cubist previously entered into that certain Commercial Services Agreement between
AstraZeneca and Cubist, dated as of July 1, 2008 (as amended as of February 26,
2009, the Agreement); and  WHEREAS, AstraZeneca and
Cubist desire to amend the Agreement to revise the Promotion Plan set forth in Exhibit M
of the Agreement.  NOW THEREFORE, in
consideration of the premises and the mutual covenants set forth herein and for
other good and valuable consideration, the receipt and sufficiency of which are
hereby acknowledged, the parties hereby agree as follows:  1.Critical Care Target Accounts.Exhibit M
to the Agreement is hereby amended so that as of the Amendment Effective Date,
the second sentence of Paragraph 1 of the Promotion Plan is hereby deleted and
replaced with the following: []*.For purposes of
a Detail to []*, Detail shall mean a Representative of
the Sales Force meeting with []*or providing an in-service for []*at which []*is in attendance, such that
the relevant characteristics of the Product are described by the Representative
consistent with the requirements of this Agreement and Applicable Law and in a
manner that is customary in the industry for the purpose of promoting a
prescription pharmaceutical product.  2.Definitions.All terms used, but not defined, in this
Second Amendment shall have the respective meanings set forth in the Agreement.  3.Construction.The principles set forth in Section 1.2
of the Agreement shall apply to this Second Amendment.  4.Effective Date; Incorporation of Terms; Continuing Effect.This Second Amendment shall be
deemed effective for all purposes as of the Amendment Effective Date.  The amendment set forth in this Second
Amendment shall be deemed to be incorporated in, and made a part of, the
Agreement, and the Agreement and this Second Amendment shall be read, taken and
construed as one and the same agreement (including with respect to the
provisions set forth in Article XVI (Miscellaneous) of the Agreement which
shall, as applicable, be deemed to apply to this Second Amendment (including
with respect to the governing law)).  Except as otherwise expressly amended by this
Second Amendment, the Agreement shall remain in full force and effect in
accordance with its terms and conditions.  5.Counterparts.This Second Amendment may be executed
simultaneously in two or more counterparts, each of which shall be deemed an
original, but all of which together shall constitute one and the same
instrument.  
 *Confidential Treatment Requested. 
Omitted portions filed with the Securities and Exchange Commission (the
Commission).


IN WITNESS
WHEREOF, the parties, intending to be bound, have caused this Second Amendment
to be executed on their behalf by their duly authorized agent as of the day and
year first above written.  ASTRAZENECA PHARMACEUTICALS LP
  
  CUBIST PHARMACEUTICALS, INC.By:
  /s/
  Marion McCourt
  
  By:
  /s/
  Michael W. BonneyName:
  Marion
  McCourt
  
  Name:
  Michael
  W. BonneyTitle:
  Vice
  President
  
  Title:
  President
  and CEO  
 *Confidential Treatment
Requested.  Omitted portions filed with
the Commission.  2