The biotech, which was the subject of intense speculation for several months after Carl Icahn bought a stake, was unable to find a buyer, even though many big drugmakers were believed to be interested in making a bid after the For Sale sign was put up official in October. So instead, Biogen will remain independent.

The news, however, sent Biogen stock plunging 26 percent in after-hours trading to about $56, after closing at $75.88. Biogen shares had a big run-up several months ago, as Wall Street speculation grew over anticipation that Biogen would be a hot item among drugmakers looking to flesh out their thinning pipelines. Pfizer, for instance, took a look last spring, but passed. Others rumors to have been interested included Glaxo, Novartis and Sanofi-Aventis. But the rumors only prompted Biogen shares to rise so much that, more recently, the biotech was seen as too rich to digest, even for desperate acquirers.

“The board emphasized that Biogen Idec’s business strategy is working and generating strong operating and financial performance,” the company said in a statement. “The board noted that it is confident that continued execution of the company’s business plan will result in attractive value for stockholders.”