Biogen Idec shares rise as proxy fight heats up

Shares rose $2.32, or 3.7 percent, to $64.57. The stock has traded between $50.63 and $84.75 over the last 52 weeks.

Icahn, in a letter to shareholders filed with the Securities and Exchange Commission Thursday, continued accusing Biogen's management of falsely portraying the sales process, which was ended Dec. 12 without a deal. Prompted by a lawsuit filed by Icahn, Biogen released documents about the process last week.

"These documents show that a number of the statements made by Biogen during this proxy contest are untrue," he said, calling the documents inconsistent with Biogen's previous public statements.

A key issue raised is whether one buyer may have walked away because it couldn't speak with Irish drug maker Elan, which shares rights to Biogen's multiple sclerosis drug Tysabri.

"It is clear from the documents they produced that at least one bidder asked to talk to Elan before they submitted a firm and binding offer," Icahn said. "The documents do not indicate whether the bidder was permitted to speak with Elan, but do indicate the bidder walked away from the process."

Icahn was the investor behind the board takeover of biotechnology company ImClone Systems Inc. in 2006 and is currently in a proxy battle with Yahoo Inc. He wants to place three people on Biogen's board of directors at the annual meeting later this month, and maintains records show Biogen's board had very little input into the sales process.

Biogen management continues to disagree.

"We believe Carl Icahn is promoting a self-serving agenda in an attempt to have three of his hand-picked nominees elected to your board," said Bruce Ross and James Mullen, Biogen's chairman and chief executive, respectively, in a letter to investors Tuesday.

They said his board nominees have not laid out a plan to improve shareholder value and believe hanging a "perpetual sale" sign over the company would only harm Biogen.