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  Exhibit 4.1    
    


 
 

  AMENDMENT TO RIGHTS AGREEMENT    
    


        THIS AMENDMENT (the "Amendment"), dated
as of the 19th day of July, 2011, to the Rights Agreement (the "Rights Agreement"), dated May 6, 2003, as amended on March 4, 2005,
January 29, 2007 and July 17, 2009, between ALLOS THERAPEUTICS, INC., a Delaware corporation (the
"Company"), and MELLON INVESTOR SERVICES LLC (the "Rights
Agent"), is being executed at the direction of the Company and shall be effective immediately prior to the Company's entry into that certain Agreement and Plan of Merger and
Reorganization (as it may be amended from time to time, the "Merger Agreement") to be entered into by and among the Company, AMAG
Pharmaceuticals, Inc., a Delaware corporation ("Parent"), and Alamo Acquisition Sub, Inc., a Delaware corporation and wholly-owned
subsidiary of Parent; provided, however, if (i) the Merger Agreement is not executed as of even
date herewith, or (ii) the Merger Agreement terminates or is terminated in accordance with the terms thereof prior to the Effective Time (as defined therein), this Amendment shall terminate, in
either such case, immediately upon the Rights Agent's receipt of written notice thereof from the Company, and shall be of no further force and effect. Capitalized terms used in this Amendment and not
otherwise defined herein shall have the meanings given them in the Rights Agreement. 



        WHEREAS, Section 27 of the Rights Agreement provides that the Company and the Rights Agent shall, if the Company so directs,
supplement or amend any provision of the Rights Agreement without the approval of any holders of the Rights, any such supplement or amendment to be evidenced by a writing signed by the Company and the
Rights Agent; and 


        WHEREAS, pursuant to Section 27 of the Rights Agreement, the Company has delivered to the Rights Agent a certificate signed by an
authorized officer of the Company certifying that the proposed amendment of the Rights Agreement is in compliance with the terms of Section 27 of the Rights Agreement. 



        NOW, THEREFORE, in consideration of the foregoing and the agreements, provisions and covenants herein contained, the parties agree as
follows: 



	1.
	Section 1(h) shall be amended and restated in its entirety as follows: 





"Excluded Stockholder" shall include each of (i) Warburg Pincus Private Equity VIII, L.P. (including its Affiliates and Associates)
("Warburg"); provided, however, that Warburg shall not be an Excluded Stockholder if, without the prior
approval of the Board of Directors, Warburg becomes the Beneficial Owner of more than 44% of the outstanding Common Shares; (ii) Baker Brothers Life Sciences, L.P. (including its
Affiliates and Associates) ("Baker"); provided, however, that Baker shall not be an Excluded Stockholder if, without the prior approval of the Board of
Directors, Baker becomes the Beneficial Owner of more than 20% of the outstanding Common Shares, and (iii) Parent, its stockholders, Merger Sub and their respective Affiliates and Associates to
the extent that any of them would otherwise become an Acquiring Person solely as the result of (x) the execution, delivery or performance of the Merger Agreement, the Parent Stockholder Voting
Agreements or the Company Stockholder Voting Agreements, (y) their acquisition or their right to acquire beneficial ownership of the Common Shares as a result of their execution of the Merger
Agreement, or (z) the consummation of the Merger or any of the other transactions contemplated by the Merger Agreement, the Company Stockholder Voting Agreements and the Parent Stockholder
Voting Agreements.  



	2.
	Section 1 shall be amended by adding the following new Section 1(s) at the end thereof: 




        (s)   The following additional terms shall have the meanings indicated: 



          (i)  "Parent" shall mean AMAG Pharmaceuticals, Inc., a Delaware
corporation. 









 


         (ii)  "Parent Stockholder Voting Agreement" shall mean each of the voting
agreements in favor of the Company to be executed concurrently with the execution of the Merger Agreement by certain stockholders of Parent. 



       (iii)  "Company Stockholder Voting Agreement" shall mean each of the voting
agreements in favor of Parent to be executed concurrently with the execution of the Merger Agreement by certain stockholders of the Company. 


        (iv)  "Effective Time" shall mean such time as the Merger shall have become
effective pursuant to the filing of a certificate of merger with the Secretary of State of the State of Delaware in accordance with the Merger Agreement. 



         (v)  "Expiration Date" shall have the meaning set forth in Section 7(a)
hereof. 


        (vi)  "Merger" shall mean the merger of Merger Sub with and into the Company
pursuant to and in accordance with the terms of the Merger Agreement. 


       (vii)  "Merger Agreement" shall mean that certain Agreement and Plan of Merger
and Reorganization to be entered into by and among the Company, Parent and Merger Sub, as amended from time to time in accordance with the terms thereof. 


      (viii)  "Merger Sub" shall mean Alamo Acquisition Sub, Inc., a Delaware
corporation and wholly-owned subsidiary of Parent.  



	3.
	Section 7(a) shall be amended and restated in its entirety as follows: 




The
registered holder of any Right Certificate may exercise the Rights evidenced thereby (except as otherwise provided herein) in whole or in part at any time after the Distribution Date upon
surrender of the Right Certificate, with the form of election to purchase on the reverse side thereof duly executed, to the Rights Agent at the office of the Rights Agent designated for such purpose,
together with payment of the Purchase Price for each one one-hundredth of a Preferred Share (or such other number of shares or other securities) as to which the Rights are exercised, at or
prior to the earliest of (i) the Close of Business on May 28, 2013 (the "Final Expiration Date"), (ii) the time at which the Rights are redeemed as provided in Section 23
hereof (the "Redemption Date"), (iii) the time at which such Rights are exchanged as provided in Section 24 hereof, or (iv) the time immediately prior to the Effective Time (but
subject to the occurrence of the Effective Time) (the earlier of (i), (ii), (iii) and (iv) being herein referred to as the "Expiration Date"), whereupon the Rights shall expire and this
Agreement shall terminate in accordance with Section 36.  



	4.
	Section 26 of the Rights Agreement is hereby amended by replacing the addresses of the Rights Agent
with the following addresses: 



 










				
	 	 	 	BNY Mellon Shareowner Services

1775 Sherman Street, Suite 2775

Denver, CO 80203

Attention: Relationship Manager

Facsimile No.: 303.764.3583
	
 	

 	
 	
with a copy to:
	
 	

 	
 	
Mellon Investor Services LLC

Newport Office Center VII

480 Washington Boulevard

Jersey City, New Jersey 07310

Attention: General Counsel

Facsimile No.: 201.680.4610






 

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	5.
	Section 30 of the Rights Agreement is hereby modified and amended to add the following sentence at the
end thereof: 



Nothing
in this Agreement shall be construed to give any holder of Rights or any other Person any legal or equitable rights, remedies or claims under this Agreement by virtue of the approval,
execution or delivery of the Merger Agreement, the Company Stockholder Voting Agreements or the Parent Stockholder Voting Agreements or the consummation of the Merger or any other transactions
contemplated by the Merger Agreement, the Company Stockholder Voting Agreements or the Parent Stockholder Voting Agreements.  



	6.
	The following is added as a new Section 35 of the Rights Agreement: 




SECTION 35.
MERGER, MERGER AGREEMENT AND VOTING AGREEMENTS. Notwithstanding anything in this Agreement to the contrary, none of (i) the execution, delivery or performance of the Merger
Agreement, the Parent Stockholder Voting Agreements or the Company Stockholder Voting Agreements nor (ii) the consummation of the Merger or any of the other transactions contemplated by the
Merger Agreement, the Company Stockholder Voting Agreements and the Parent Stockholder Voting Agreements shall result in (x) Parent, its stockholders, Merger Sub and their respective Affiliates
and Associates being the Beneficial Owner of Common Shares, (y) the deemed occurrence of either a Shares Acquisition Date or a Distribution Date or (z) the separation of the Rights from
the Common Shares.  



	7.
	The following is added as a new Section 36 of the Rights Agreement: 





SECTION 36.
TERMINATION UPON EXPIRATION DATE. Notwithstanding anything to the contrary in this Agreement, upon the Expiration Date and without any further action by the Rights Agent, the
Company, Parent, Merger Sub or any current or former holder of Rights, this Agreement, the Rights, and any right to exercise the Rights provided for hereunder shall terminate and be void and of no
further force or effect.  



	8.
	The Rights Agreement shall not otherwise be supplemented or amended by virtue of this Amendment, but shall
remain in full force and effect. This Amendment may be executed in one or more counterparts, including by facsimile or PDF copy, all of which shall be considered one and the same amendment and each of
which shall be deemed an original.



	9.
	This Amendment shall be deemed to be a contract made under the laws of the State of Delaware and for all
purposes shall be governed by and construed in accordance with the laws of such State applicable to contracts to be made and performed entirely within such State; provided, however, that all
provisions regarding the rights, duties and obligations of the Rights Agent shall be governed by and construed in accordance with the laws of the State of New York applicable to contracts made and to
be performed entirely within such State. 



[Remainder
of Page Intentionally Left Blank] 


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        IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be duly executed and attested, all as of the day and year first above
written. 

 






 



							
	 ALLOS THERAPEUTICS, INC.	 	 MELLON INVESTOR SERVICES LLC, AS

RIGHTS AGENT
	
 By:	
 	
/s/ MARC GRABOYES







 	
 	
By:	
 	
/s/ TIFFANY J. SKILES







 
	
 Name:	
 	
Marc Graboyes








 	
 	
Name:	
 	
Tiffany J. Skiles







 
	
 Title:	
 	
Senior Vice President, General Counsel & Secretary







 	
 	
Title:	
 	
Client Relationship Executive







 




 

 SIGNATURE
PAGE TO AMENDMENT TO RIGHTS AGREEMENT 


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Exhibit 4.1


AMENDMENT TO RIGHTS AGREEMENT