Acceleron Pharma Inc. (NASDAQ:XLRN), a clinical stage biopharmaceutical company focused on the discovery, development and commercialization of novel protein therapeutics for cancer and rare diseases, today announced that it has filed a registration statement on Form S-1 with the U.S. Securities and Exchange Commission (“SEC”) relating to the proposed underwritten public offering of its common stock. All shares of common stock to be sold in the offering will be offered by Acceleron. The number of shares to be offered and the price for the offering have not been determined. Citigroup and Leerink Partners LLC will act as joint book-running managers for the offering. Piper Jaffray & Co. will act as lead manager and JMP Securities will act as co-manager for the offering. A registration statement relating to these securities has been filed with the SEC, but has not yet become effective. These securities may not be sold, nor may offers to buy be accepted, prior to the time the registration statement becomes effective. This press release shall not constitute an offer to sell or a solicitation of an offer to buy, nor shall there be any sale of these securities in any state or jurisdiction in which such offer, solicitation or sale would be unlawful, prior to registration or qualification under the securities laws of any such state or jurisdiction. The offering will be made only by means of a prospectus. When available, copies of the preliminary prospectus relating to the offering may be obtained from Citigroup, c/o Broadridge Financial Solutions, 1155 Long Island Avenue, Edgewood, NY, 11717, or by email at firstname.lastname@example.org, or by phone at 800-831-9146; or Leerink Partners LLC, Attention: Syndicate Department, One Federal Street, 37th Floor, Boston, MA, 02110, or by email at Syndicate@Leerink.com, or by phone at 800-808-7525. About Acceleron Acceleron is a clinical stage biopharmaceutical company focused on the discovery, development and commercialization of novel protein therapeutics for cancer and rare diseases. The company is a leader in understanding the biology of the TGF-β protein superfamily, a large and diverse group of molecules that are key regulators in the growth and repair of tissues throughout the human body, and in targeting these pathways to develop important new medicines. Acceleron has built a highly productive R&D platform that has generated innovative clinical and preclinical protein therapeutic candidates with novel mechanisms of action. These protein therapeutic candidates have the potential to significantly improve clinical outcomes for patients with cancer and rare diseases.