FOURTH AMENDMENT TO LEASE

Exhibit 10.34

FOURTH AMENDMENT TO LEASE

        THIS FOURTH AMENDMENT TO LEASE (this "Fourth Amendment") is made as of the 25th day of October, 2007 (the "Fourth 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 (Suite 2201-55) and fourth (Suite 4201-55) 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"), and by a Second Amendment to Lease between Landlord and Tenant dated as of November 18, 2005 (the "Second Amendment"), and by a Third Amendment to Lease between Landlord and Tenant dated as of June 20, 2007 (the "Third 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 83,097 rentable square feet (the "Existing Premises"). The Existing Premises consist of Suites 2201-55, 2200-55, 3000-55, 4201-55 and 4200-55; and

        WHEREAS, by letter dated as of April 27, 2006, and pursuant to the Second Amendment, Tenant elected to include Suite 2200-55 (also known as the Comet Space) in the Existing Premises for the remainder of the Lease Term; and

        WHEREAS, Landlord and Tenant now desire to further amend the Lease to, among other things, expand the size of the Existing Premises by adding thereto approximately 25,405 rentable square feet of space in Suite 4600-45 on the fourth floor of the Building (the "Additional Fourth Floor Space"), and to adjust the rent and certain provisions, 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:

• 1.

  Defined Terms.     All of the foregoing recitals are true and correct. Unless otherwise defined herein, all capitalized terms used in this Fourth Amendment shall have the meanings ascribed to them in the Lease, the Lease shall be amended to incorporate any additional definitions provided for in this Fourth Amendment, and all references in the Lease to the "Lease" or "this Lease" or "herein" or "hereunder" or similar terms or to any section thereof shall mean the Lease, or such section thereof, as amended by this Fourth Amendment.

• 2.

  Additional Terms and Definitions.     (a) From and after the Fourth Amendment Effective Date, the following terms set forth in "Article 1 Reference Data" of the Lease are hereby amended or added, as applicable, to have the following meanings:

• • (b)

    From after the Fourth Amendment Effective Date, the term "Annual Rent" for the Premises shall be as set on Schedule I to this Fourth Amendment. Notwithstanding the foregoing, so long as the Lease remains in full force and effect, and so long as no Actionable Event of Default (as defined in the Third Amendment) shall exist under the Lease, Landlord will waive the requirement that Tenant pay Annual Rent on the Additional Fourth Floor Space for the period commencing on the Fourth Amendment Effective Date and ending on the one hundred eightieth (180 ^th ) day after the Fourth Amendment Effective Date.
    
    

  3.

  Furniture.     In consideration of the terms and covenants contained in this Fourth Amendment, Landlord hereby conveys, grants, sells and transfers to Tenant as of the Fourth Amendment Date, without any warranty or representation whatsoever other than as stated in Section 15 hereto (including without limitation any representation or warranty as to condition or fitness for intended use) all of the Landlord's right, title and interest in and to the furniture and furnishings (the "Furniture") located in Suite 3000-55, located on the third floor of the 55

2

• • Hayden Avenue portion of the Building (the "Third Floor Space"), which was added to the Premises by the Third Amendment. Such Furniture is described on Schedule II to this Fourth Amendment, which Landlord in good faith believes to be true and correct as of the Fourth Amendment Date. Landlord shall have no liability for any inaccuracy between Schedule II and the actual number or description of Furniture items as of the Fourth Amendment Effective Date. By executing this Fourth Amendment, Tenant accepts such transfer and the Furniture on the terms and conditions stated above.

  4.

  Operating Expenses and Real Estate Taxes.     From and after the Fourth Amendment Effective Date, Tenant's obligations under Section 4.2 of the Lease to pay Operating Expenses with respect to the Additional Fourth Floor Space shall be computed using the calendar year ending December 31, 2008 as a base year; and Tenant's obligations under Section 4.2 of the Lease to pay increases in Real Estate Taxes with respect to the Additional Fourth Floor Space shall be computed using the fiscal year ending June 30, 2008 as the base year.
  
  

  5.

  Effective Date; Delivery and Condition .    (a) The "Fourth Amendment Effective Date" shall be the later to occur of (i) November 1, 2007 and (ii) the date on which Motorola, Inc. (the "Existing Tenant") vacates the Additional Fourth Floor Space and Landlord delivers possession thereof to Tenant. If the Fourth Amendment Effective Date is delayed due solely to a holdover by the Existing Tenant, and if (without imposing on Landlord any obligation to do so) Landlord actually recovers any premium rent or other additional amount in the nature of rent from the Existing Tenant solely on account of such holding over, Landlord shall pay Tenant fifty percent (50%) of any net excess rent ( i.e. , after deducting Landlord's reasonable costs and expenses in recovering the same) above the Existing Tenant's base rent, actually received by Landlord due to such holdover. Such payment shall be made within thirty (30) days after Landlord's receipt of such excess rent from the Existing Tenant.
  
  

  (b)

  Tenant acknowledges that, except as explicitly provided in this Fourth Amendment and the Lease, it is leasing the Additional Fourth Floor Space in its current AS IS condition, without any representation or warranty whatsoever on the part of Landlord. Tenant currently occupies the Existing Premises and is fully familiar with their condition and that of the common areas of the Building, and Tenant acknowledges that, to the best of Tenant's knowledge (upon reasonable investigation and inquiry), the Existing Premises and the Additional Fourth Floor Space are in good condition and suitable for Tenant's uses. Without limiting the foregoing, Tenant agrees that Landlord has no obligation to perform any work in or to either the Existing Premises or the Additional Fourth Floor Space to prepare the same for Tenant's continued use and occupancy.
  
  

  (c)

  Landlord acknowledges that Tenant desires to make certain alterations or improvements in the Additional Fourth Floor Space to make the same more suitable for Tenant's occupancy. Such alterations or improvements may include tenant improvements to the Additional Fourth Floor Space, including to the bathrooms within the Additional Fourth Floor Space, installation of fixtures in the Additional Fourth Floor Space, and architectural and engineering expenses in connection therewith (collectively, the "Additional Fourth Floor Improvements"). All Additional Fourth Floor Improvements shall be undertaken by Tenant in strict accordance with the applicable requirements of the Lease (including without limitation Sections 3.3 and 3.4). The Additional Fourth Floor Improvements shall be deemed substantially complete on that date on which the Additional Fourth Floor Improvements have been completed except for