EXHIBIT 10.25

SECOND
AMENDMENT TO LEASE

THIS
SECOND AMENDMENT TO LEASE (this "Amendment") is made as of the 18th day of November, 2005 (the "Second Amendment Date"), by and between THE REALTY ASSOCIATES FUND
VI, L.P., a Delaware limited partnership ("Landlord") and CUBIST PHARMACEUTICALS, INC., a Delaware corporation ("Tenant").

RECITALS:

WHEREAS,
by a lease (the "Original Lease") dated as of January, 2004, California State Teachers' Retirement System ("Calsters") leased to Tenant approximately 15,475 rentable square feet
of space, consisting of a portion of the second and fourth floors in the building known as 45-55 Hayden Avenue, Lexington, Massachusetts (the "Building"); and

WHEREAS,
Landlord has succeeded to the interests of Calsters as landlord under the Lease; and

WHEREAS,
the Original Lease has been amended by a First Amendment to Lease between Landlord and Tenant, dated as of September 29, 2005 (the "First Amendment;" the Original Lease,
as so amended, being referred to as the "Lease"), pursuant to which the size of the premises demised under the Original Lease was increased to 46,928 rentable square feet (the "Existing Premises");
and

WHEREAS,
Landlord and Tenant now desire to further amend the Lease to, among other things, temporarily expand the size of the Existing Premises by adding thereto approximately 6,150
rentable square feet of space on the second floor of the Building (the "Comet Space"), and to temporarily adjust the rent and certain provisions, and to provide an option for the Tenant to lease the
Comet Space for a longer term, all on the terms and conditions set forth below.

NOW,
THEREFORE, in consideration of the mutual covenants herein contained, and for other good and valuable consideration, the receipt and sufficiency of which are hereby acknowledged,
and intending to be legally bound hereby, Landlord and Tenant hereby agree as follows:



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PREMISES:

The space in the Building, including the entire fourth floor and the space located on the second floor of the 55 Hayden Avenue portion of the Building, as shown onExhibit A-2attached hereto and incorporated herein.RENTABLE FLOOR AREA OF THE PREMISES:

Approximately 53,078 square feet, of which 40,173 square feet consists of the entire fourth floor of the 55 Hayden Avenue portion of the Building and 12,905 square feet are located on the second floor of the Building.ANNUAL RENT:

The Annual Rent payable under the Lease shall be as set forth on Schedule I to the First Amendment, plus $11,787.50 per month from December 1, 2005 through May 31, 2006 for the Comet Space.




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RENTAL PERIOD

TOTAL ANNUAL RENT

MONTHLY PAYMENT

RENTAL RATE/SF6/1/064/30/07

$
140,415.00

$
11,787.50

$
23.005/1/074/30/08

$
144,525.00

$
12,043.75

$
23.505/1/084/30/09

$
147,600.00

$
12,300.00

$
24.005/1/094/30/10

$
155,287.50

$
12,940.63

$
25.255/1/104/30/11

$
158,362.50

$
13,196.88

$
25.755/1/114/30/12

$
161,437.50

$
13,453.13

$
26.255/1/124/30/13

$
166,050.00

$
13,837.50

$
27.005/1/134/30/14

$
173,737.50

$
14,478.13

$
28.255/1/144/30/15

$
181,425.00

$
15,118.75

$
29.505/1/154/30/16

$
186,037.50

$
15,503.13

$
30.25




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IN
WITNESS WHEREOF, the undersigned have hereunto se their hands and seals as of the date first above written.

| | LANDLORD:                                                          
| | -------------------------------------------------------------------
| | The Realty Associates Fund VI, L.P.,
a Delaware limited partnership
| | By:                                                                
| |                                                                    
| |                                                                    
| |                                                                    
| |                                                                    
| | By:                                                                
| |                                                                    
| |                                                                    
| | TENANT:                                                            
| | CUBIST PHARMACEUTICALS, INC.                                       
| | By:                                                                
| |                                                                    

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Exhibit A-2

[Floor
Plans]



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SCHEDULE
1
List of Equipment

Reception Area:



Board Room, Main:



Conference Roomfirst office



Conference Areafront of office



Offices (5):



Cubicles 8x8 (19) wired for electric and data:



Kitchen:



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Miscellaneous:



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SCHEDULE
2

RIGHTS
OF EXISTING BUILDING TENANTS

|                                                               |  |                                                                                                                                                                                                                       
|-------------------------------------------------------------- |  | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|Celerant                                                       |  | Option to Extend                                                                                                                                                                                                      
|8,017 sf2nd Fl (45)
Expiration 8/31/07                        |  | One 5 year term (thru August 31, 2012); 12 mos. notice prior to expiration of current term required                                                                                                                   
|Summit Mortgage                                                |  | Option to Extend                                                                                                                                                                                                      
|2,805 sf2nd Fl (45)
Expiration 2/28/09                        |  | One 5 year term (thru February 28, 2014); 9 mos. notice prior to expiration of current term required                                                                                                                  
|Motorola                                                       |  | Option to Extend                                                                                                                                                                                                      
|25,405 sf2nd Fl (45)
30,019 sf3rd Fl (55)
Expiration 4/30/07 |  | One 3 year term (thru April 30, 2010); 9 mos. notice prior to expiration of current term required                                                                                                                     
|Goodrich, LLC                                                  |  | Option to Extend                                                                                                                                                                                                      
|10,495 sf3rd Fl (55)
Expiration 11/30/09                      |  | One 7 year term (thru November 30, 2016); 12 mos. notice prior to expiration of current term required                                                                                                                 
|Aon Consulting                                                 |  | Option to Extend                                                                                                                                                                                                      
|5,528 sf2nd Fl (45)
Expiration 7/31/06                        |  | One 5 year term (thru July 31, 2011); 12 mos. notice prior to expiration of current term required                                                                                                                     
|Spaulding and Slye                                             |  | Option to Extend                                                                                                                                                                                                      
|14,092 sf2nd Fl (55)
Expiration 3/31/15                       |  | Two extension of 5 year terms (thru March 31, 2020 and March 31, 2025, respectively); each on 9 mos. notice prior to expiration of current term required                                                              
|Spaulding and Slye                                             |  | First Right to Lease                                                                                                                                                                                                  
|                                                               |  | During the term of Spaulding and Slye's lease to the 14,092 sf on the 2nd floor of the 55 Hayden Avenue portion of the Building, Spaulding and Slye holds a first right to lease the following spaces in the
Building:
|                                                               |  |  8,017 sf2nd Fl (45) (Celerant space)                                                                                                                                                                               
|                                                               |  |  2,805 sf2nd Fl (45) (Summit Mortgage space)                                                                                                                                                                        
|                                                               |  |  5,528 sf2nd Fl (45) (Aon Consulting space)                                                                                                                                                                         
|                                                               |  |  3,089 sf2nd Fl (45) (FCG space)                                                                                                                                                                                    
|                                                               |  | Spaulding and Slye must respond to the Landlord's notice of any such space becoming available within 14 days of such notice.                                                                                          

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