SECOND AMENDMENT TO LEASE

Exhibit 10.1

SECOND AMENDMENT TO LEASE

This Second Amendment to Lease (the “ Second Amendment ”) is hereby entered into as of the 27th day of August, 2007 (the “ Effective Date ”) by and between W2007 CPD REALTY, L.L.C., a Delaware limited liability company having an address c/o Archon Group, L.P., 99 High Street, Floor 28, Boston, Massachusetts  02110 (“ Landlord ”), and AMAG Pharmaceuticals, Inc., formerly known as Advanced Magnetics, Inc., a Delaware corporation having an address at 125 CambridgePark Drive, Cambridge, Massachusetts 02140 (“ Tenant ”).

WHEREAS, CambridgePark 125 Realty Corporation (the “ Original Landlord ”), as landlord, and Tenant, as tenant, entered into that certain Lease dated as of February 28, 2006 (the “ Original Lease ”) by which the Original Landlord leased to Tenant and Tenant leased from the Original Landlord approximately 8,230 square feet of office space on the sixth (6 th ) floor of the building (the “ Building ”) located at and numbered 125 CambridgePark Drive, Cambridge, Massachusetts 02140 as more particularly described in the Original Lease (the “ Original Premises ”).

WHEREAS, the Original Lease was amended by that certain First Amendment to Lease by and between the Original Landlord, as landlord, and Tenant, as tenant, dated November 29, 2006 (the “ First Amendment ”), by which the Tenant leased additional office space from the Original Landlord consisting of approximately 8,154 square feet of office space on the second (2 nd ) floor of the Building (the “ First Amendment Premises ”).

WHEREAS, the Original Lease, as amended by the First Amendment, is hereinafter referred to as the “Lease”.

WHEREAS, Landlord has succeeded to the interest of the Original Landlord as owner of the Building and as landlord under the Lease.

WHEREAS, the current term of the Lease expires on February 28, 2009.

WHEREAS, Landlord desires to lease to Tenant and Tenant desires to lease from Landlord additional space on the first (1 st ) and sixth (6 th ) floors of the Building in accordance with the terms and provisions of this Second Amendment.

NOW, THEREFORE, in consideration of the premises and the mutual agreements contained herein and in the Original Lease, Landlord and Tenant hereby agree as follows:

A.            SUITE B PREMISES

1.             Landlord hereby leases to Tenant and Tenant hereby leases from Landlord the so-called Suite B on the first (1 st ) floor of the Building consisting of 5,801 rentable square feet of floor area, as shown cross-hatched on Exhibit B attached hereto (the “ Suite B Premises ”), upon the same terms and conditions set forth in the Lease for the Current Premises, except as expressly otherwise provided in this Second Amendment.  As used herein, the phrase “Suite B

Premises Commencement Date” shall mean September 1, 2007.  As used herein, the phrase “Suite B Premises Rent Commencement Date” shall mean the date that is one (1) month after the Suite B Premises Commencement Date.  Notwithstanding anything in the Lease to the contrary, effective on and after the Suite B Premises Commencement Date, the word “Premises,” whenever such word appears in the Lease as amended by this Second Amendment shall mean, collectively, the Original Premises, the First Amendment Premises and the Suite B Premises.

2.             Prior to occupying the Suite B Premises, Tenant shall execute and deliver to Landlord a letter substantially in the form of Exhibit C attached hereto confirming (i) the Suite B Premises Commencement Date, and (ii) that Tenant has accepted the Suite B Premises; however, the failure of the parties to execute such letter shall not defer the Suite B Premises Commencement Date or otherwise invalidate the Lease or this Second Amendment.

3.             Notwithstanding anything in the Lease to the contrary, effective on and after the Suite B Premises Rent Commencement Date, the Annual Rent (as defined in the Original Lease) for the Suite B Premises shall be the following amounts for the following periods of time:

*                     Subject to rent abatement provision in Exhibit D .

4.             Commencing on the Suite B Premises Rent Commencement Date, Tenant shall pay to Landlord, as additional rent for the Suite B Premises, 3.15% of Annual Operating Costs (as defined in the Original Lease) for each calendar year during the Term in excess of the Annual Operating Costs for the Suite B Base Year.  As used herein, the “Suite B Base Year” shall mean calendar year 2007, except that,  with respect to Real Estate Taxes only, the term “Suite B Base Year” shall mean fiscal year 2008 (i.e., July 1, 2007 — June 30, 2008).  The payments of additional rent required to be paid by Tenant under this paragraph shall be paid in the manner, at the times and otherwise in accordance with the provisions of Sections 4.2 and 4.3 of the Lease.

5.             Notwithstanding anything in the Lease to the contrary, commencing on the Suite B Premises Commencement Date, electricity furnished to the Suite B Premises shall be paid for by Tenant in accordance with the terms and provisions of Section 4.4 of the Lease.  Tenant and Landlord agree that all computer rooms and equipment which require more electricity than described in Section 4.4 of the Lease will be separately metered and paid directly by the Tenant.

6.             Notwithstanding anything in the Lease to the contrary, commencing on the Suite B Premises Commencement Date, the number of Base Cards (as defined in the Lease) shall be increased from 49 to 67, 22 of which are for spaces located in the Blue Lot (as defined in the

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Lease), and 47 of which are for spaces located in the Red Lot (as defined in the Lease) and the number of Additional Spaces (as defined in the Lease) shall be increased from 16 to 22.

7.             Tenant’s taking possession of Suite B Premises shall be conclusive evidence that the Suite B Premises is in good order and satisfactory condition at such time.  No agreement of Landlord to alter, remodel, decorate, clean or improve the Suite B Premises and no representation or warranty regarding the condition of the Suite B Premises or the suitability of the Suite B Premises for Tenant’s proposed use thereof have been made by or on behalf of Landlord or relied upon by Tenant in connection with this Second Amendment, except as otherwise provided in Exhibit D attached hereto.

B.            SUITE A PREMISES

8.             Landlord hereby leases to Tenant and Tenant hereby leases from Landlord the so-called Suite A on the sixth (6 th ) floor of the Building consisting of 2,426 rentable square feet of floor area, as shown cross-hatched on Exhibit A attached hereto (the “ Suite A Premises ”), upon the same terms and conditions set forth in the Lease for the Current Premises, except as expressly otherwise provided in this Second Amendment.  As used herein, the phrase “Suite A Premises Commencement Date” shall mean the date on which Landlord delivers vacant possession of the Suite A Premises to Tenant with the Suite A Work (defined below) complete; provided, that in no event shall the Suite A Premises Commencement Date or the date of completion of the Suite A Work be later than November 15, 2007.  Landlord agrees to perform, at Landlord’s sole expense, the following work in the Suite A Premises (the “Suite A Work”):  (i) repaint (two (2) coats) all walls in the Suite A Premises in building standard colors selected by Tenant; and (ii) recarpet the entire Suite A Premises with building standard carpet in a color selected by Tenant.  As used herein, the phrase “Suite A Premises Rent Commencement Date” shall mean the date that is one (1) month after the Suite A Premises Commencement Date.  Notwithstanding anything in the Lease to the contrary, effective on and after the Suite A Premises Commencement Date, the word “Premises,” whenever such word appears in the Lease as amended by this Second Amendment shall mean collectively, the Original Premises, the First Amendment Premises, the Suite B Premises and the Suite A Premises.

9.             Prior to occupying the Suite A Premises, Tenant shall execute and deliver to Landlord a letter substantially in the form of Exhibit C attached hereto confirming (i) the Suite A Premises Commencement Date, and (ii) that Tenant has accepted the Suite A Premises; however, the failure of the parties to execute such letter shall not defer the Suite A Premises Commencement Date or otherwise invalidate the Lease or this Second Amendment.  Such letter may incorporate a punchlist if any of the Suite A Work is not complete at such time.

10.           Notwithstanding anything in the Lease to the contrary, effective on and after the Suite A Premises Rent Commencement Date, the Annual Rent (as defined in the Original Lease) for the Suite A Premises shall be the following amounts for the following periods of time:

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11.           Commencing on the Suite A Premises Rent Commencement Date, Tenant shall pay to Landlord, as additional rent for the Suite A Premises, 1.32% of Annual Operating Costs (as defined in the Origi