Exhibit 10.59  CONFIDENTIAL TREATMENT  SIXTH AMENDMENT TO THE COMMERCIAL SERVICES AGREEMENT  This Sixth Amendment to the Commercial Services
Agreement (this Sixth Amendment) is made this
11thday of December, 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, May 20,
2009, September 30,2009, October 15,
2009 and October 16, 2009, the Agreement);  WHEREAS, Section 6.1(a) of the Agreement
provides that the []*;  WHEREAS, the parties desire to amend the Agreement to
establish []* Sales baselines and a manner of compensating Cubist for its
activities under the Agreement for the period from January 1, 2010 through
June 30, 2010 (the Six Month Period);
and  WHEREAS, the parties desire for the Agreement to
remain in effect until the end of the Six Month Period (or such alternate
period as is mutually agreed by the parties in writing as set forth in this
Sixth Amendment).  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:  I.Annual Baseline Sales for
the Six Month Period.Exhibit A of the Agreement is hereby
amended so that Annual Baseline Sales for the Six Month Period shall equal []*.  The Quarterly Baseline Sales for each
Calendar Quarter therein shall equal []*.  For
all purposes under Article 6 of the Agreement, the Six Month Period shall
be treated as if it were a Calendar Year. 
If the Term ends at the end of the Six Month Period, then the last
sentence of Section 6.2(a) shall not apply.  II.Calculation of Annual
Amount Due for the Six Month Period.Exhibit A of the Agreement is hereby
amended so that the Annual Amount Due for the Six Month Period shallequal the
amount set forth in the chart below, determined based on the level of []*Sales achieved during the
Six Month Period. For clarity, without limiting any of Cubists
rights under the Agreement (as amended by this Sixth Amendment),the Annual Amount Due calculations otherwise set forth in Exhibit A
shall not apply and the maximum compensation due to Cubist under Section 6.2
of the Agreement for its activities during the Six Month Period shall in no
event exceed Nine Million U.S. Dollars ($9,000,000).  
 *Confidential
Treatment Requested.  Omitted portions
filed with the Securities and Exchange Commission (the Commission).


Calculation
of Annual Amount Due for Six
Month Period (All figures in millions)  []* Sales for Six Month Period
  
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  4  III.Calculation of Quarterly Amount Duefor the Six Month Period.Exhibit A is hereby
amended so that Quarterly Amount Due is defined, solely for purposes of the
Calendar Quarters in the Six Month Period, as follows:  Quarterly Amount Due means, subject to Section 6.2(a) and (f), (a) for
the first Calendar Quarter of Calendar Year 2010, []*, and (b) for the
second Calendar Quarter of Calendar Year 2010, []*.  By way of illustration, []* Sales during the Six Month Period
are []*, then Cubist shall receive []*
for the first Calendar Quarter of 2010, and []* for the second Calendar Quarter of 2010, for a total payment to
Cubist equal to []*.  For clarity, the invoicing and timing of the
Quarterly Amount Due payments shall be in accordance with Section 6.2(b) of
the Agreement.  IV.2009
Significant Market Events.If Cubist desires an adjustment to Annual Baseline Sales for 2009
pursuant to Section 6.1(b) of the Agreement due to a Significant
Market Event, Cubist shall request such adjustment in writing no later than January 31,
2010.  If Cubist so requests an
adjustment to Annual Baseline Sales for 2009, then AstraZeneca may terminate
the Agreement effective immediately by written notice of termination under this
Paragraph IV to Cubist at any time on or after the date of such request, but no
later than February 14, 2010.  In
the event the Agreement is terminated pursuant to this Paragraph IV, []*.  V.Expiration
of Agreement as of June 30, 2010.Notwithstanding Section 6.1(a) and
the fact that the []*, the Agreement shall not terminate pursuant
to Section 6.1(a) []*.  Section 15.1 of the Agreement is hereby
amended so that the language therein is replaced with the following
language:  The term of this Agreement
shall commence on the Effective Date and shall continue through June 30,
2010, unless earlier terminated pursuant to Section 15.2 or any other
applicable provision of this Agreement (the Term),
provided that, beginning no later than []*, 2010,
AstraZeneca and Cubist shall negotiate []*the manner in
which Cubist is to be compensated for activities to be performed by Cubist
during the period from July 1 through December 31, 2010, and if the parties
reach agreement on such terms on or prior to May 1, 2010, the Term shall
be  
 *Confidential Treatment Requested. 
Omitted portions filed with the Commission.  2


extended
until December 31, 2010, unless further extended by mutual written
agreement of AstraZeneca and Cubist.  VI.Reporting and Audit Rights.In light of the basis for
calculating the Annual Amount Due for the Six Month Period, AstraZeneca shall
have no obligation to report, and Cubist shall have no right to audit, the []*
with respect to the Six Month Period; provided that, for the avoidance of
doubt, AstraZeneca shall continue to have the obligation to report, and Cubist
shall have the right to audit, the []*amounts and calculations provided by AstraZeneca for
such periods.  VII.Definitions.All terms used, but not defined, in this Sixth Amendment shall have the
respective meanings set forth in the Agreement.  VIII.Construction.The principles set forth in Section 1.2 of the Agreement shall
apply to this Sixth Amendment.  IX.Effective Date; Incorporation of
Terms; Continuing Effect.This Sixth
Amendment shall be deemed effective for all purposes as of the Amendment
Effective Date.  The amendments set forth
in this Sixth Amendment shall be deemed to be incorporated in, and made a part
of, the Agreement, and the Agreement and this Sixth 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 Sixth Amendment
(including with respect to the governing law)). 
Except as otherwise expressly amended by this Sixth Amendment, the
Agreement shall remain in full force and effect in accordance with its terms
and conditions.  X.Counterparts.This Sixth 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.  [The remainder of this page has been
intentionally left blank.]  
 *Confidential Treatment Requested. 
Omitted portions filed with the Commission.  3


IN WITNESS WHEREOF, the parties, intending to be bound, have caused this
Sixth Amendment to be executed on their behalf by their duly authorized agent
as of the Amendment Effective Date.   ASTRAZENECA
  PHARMACEUTICALS LP
  
  CUBIST PHARMACEUTICALS, INC.By:
  /s/ Rich Fante
  
  By:
  /s/ Robert J. PerezName:
  Rich Fante
  
  Name:
  Robert J. PerezTitle:
  President
  
  Title:
  Chief Operating Officer
  [Sixth Amendment
Signature Page]  
 *Confidential Treatment Requested. 
Omitted portions filed with the Commission.  4