NEW YORK (Reuters) -- Bristol-Myers Squibb Co (BMY.N) has offered to buy ImClone Systems Inc (IMCL.O) for $60 a share, valuing its biotech partner at $5.2 billion in a deal to strengthen its grip on the fast-growing Erbitux cancer drug.

ImClone shares jumped 37.7 percent to $63.93 on Thursday, well above the offer price, reflecting the expectation that the company will command a higher offer.
""I think they may have to pay closer to a 50 percent premium,"" said Summer Street Research analyst Carol Werther. ""ImClone has a superb pipeline, and I think you have to value that somehow.""
The unsolicited offer, which represents a premium of roughly 30 percent over Wednesday's closing price, marks the latest in a spate of pharmaceutical-biotech deals, including Roche Holding AG's (ROG.VX) recent $43.7 billion bid for the part of Genentech Inc (DNA.N) it doesn't already own.
Drug makers have been eager to buy biotech assets to replenish dry pipelines as they endure patent expirations on their top medicines.
Shares of other biotechnology companies with pharmaceutical partners, including Amylin Pharmaceuticals Inc (AMLN.O) and Onyx Pharmaceuticals (ONXX.O), rose sharply after news of Bristol's offer.
A buyout would be the latest twist in ImClone's colorful history. Stock trades in late 2001, based on insider news about Erbitux, landed ImClone's original CEO, Sam Waksal, and his friend Martha Stewart in jail.
According to a regulatory filing, Bristol Chief Executive James Cornelius made the offer to Carl Icahn, the billionaire investor who is also ImClone's chairman. Few investors expect Icahn to accept the bid as is.