Kevin Sharer, CEO and chairman of Amgen, will leave the world’s largest biotech at the end of 2012, following more than a decade at the company’s helm.

In addition, Roger Perlmutter, Amgen’s head of research will also retiring, though he’ll aid the company as a consultant through February 2012.

During Sharer’s tenure, Amgen grew from $3.6 billion in revenue to a company with revenues approaching $16 billion today. The company succeeded in marketing new drugs to treat anemia, colorectal cancer, osteoporosis, and to defend against chemotherapy-related infections. But it also faced significant challenges over safety concerns about its anemia drugs and criticisms over lower-than-expected research and development productivity. Sharer has also attracted criticism for securing a much larger-than-average package of executive pay and perks.

Robert Bradway, currently Amgen’s president and COO, will replace Sharer in the top job on May 23, 2012. To smooth the transition, Sharer will remain as chairman of the Amgen’s board until the end of 2012, at which time he will retire. The company’s board plans to elect Bradway as chairman at that time when it will also elect a lead independent director.

Prior to joining Amgen, Bradway was a managing director at Morgan Stanley in London where he had responsibility for the firm's banking department and corporate finance activities in Europe.

Sean Harper, now Amgen’s SVP of global development and CMO, will succeed Perlmutter as EVP of research and development, taking responsibility for Amgen's global research and development functions.