Executive Employment Living Arrangements Agreement

Exhibit 10.3

April 13, 2009

Santosh J. Vetticaden, Ph.D., M.D.

Dear Santosh,

As discussed, this letter amends and restates Exhibit A of your November 12, 2008 offer letter.   This amendment is prompted by your plan to rent out your house in San Ramon, California to a third party for three years after being unable to sell it for a reasonable price and your desire to purchase a house in the greater Boston area as quickly as possible.  The primary differences between Exhibit A of your November 12, 2008 offer letter and Exhibit A of this letter are the reduction of Cubist’s obligation to provide you with temporary living/duplication housing assistance from 12 months to 8 months (from 12/31/09 back to 8/31/09) and the elimination of Cubist’s obligation to cover any of the closing costs related to the sale of your house in San Ramon, California, in exchange for a payment from Cubist to you of $87,250 (along with a gross-up on taxes that arise from this payment) to be used by you to purchase a house in the greater Boston area.  This payment will, in part, offset the losses resulting from the planned rental of your California house.  The amount of this payment is equal to the approximate value of the decrease in Cubist’s obligation to provide you with the housing assistance and closing costs described in this letter (and the tax gross-up related to such obligations).  By signing this you agree, should you decide to sell your home in California Cubist is not obligated to pay closing costs. A

Exhibit A attached to this letter supersedes and replaces Exhibit A of your November 12, 2008 offer letter in its entirety and is incorporated by reference into this letter.  All of the other terms and provisions of your November 12, 2008 offer letter remain in full force and effect.

I acknowledge and agree to the terms and conditions of this letter.