On Sunday, May 16, 2010 OSI agreed to be acquired by Japan-based, TSE-listed Astellas Pharma for $4.0 billion.

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.

[6][1] OSI had also made a foray into the ophthalmology market through a marketing agreement with Pfizer over Macugen (Pegaptanib) for Age-related macular degeneration; however, acquisition of the firm Eyetech, meant to provide control over this product and diversify the company, was unsuccessful, ending in divestiture.

[7][8] In mid-2007, OSI's revenues were based primarily on proceeds from Tarceva sales (which are shared with Genentech and Hoffmann–La Roche) and royalty payments related to dipeptidyl-peptidase IV inhibitor intellectual property.

[7][9] Tarceva is a small molecule inhibitor of the epidermal growth factor receptor (EGFR) and is the only EGFR inhibitor to have demonstrated the ability to improve overall survival in advanced non-small cell lung cancer and advanced pancreatic cancer.