OSI Pharmaceuticals, Inc. was an American pharmaceutical company formerly based on Long Island, New York with facilities in Colorado, New Jersey and the United Kingdom. On Sunday, May 16, 2010 OSI agreed to be acquired by Japan-based, TSE-listed Astellas Pharma for $4.0 billion.[3] The deal was closed on June 9, 2010. The company closed its last facilities on Long Island in May 2013.[4] OSI had specialized in the discovery and development of molecular targeted therapies. Though oncology was the top priority for OSI, research and development targeting type 2 diabetes and obesity had been conducted through their U.K. subsidiary Prosidion Limited.[5][6] OSI had also made a foray into the ophthalmology market through a marketing agreement with Pfizer