UPDATE 4-Biogen puts itself up for sale; shares surge

(Adds details on Icahn offer)

BOSTON, Oct. 12 (Reuters) - Biogen (BIIB.O: Quote, Profile, Research, Stock Buzz) (BIIB.O: Quote, Profile, Research, Stock Buzz) Idec Inc (BIIB.O: Quote, Profile, Research, Stock Buzz), one of the world's biggest biotechnology companies, has put itself up for sale as it wrestles with slowing growth for its flagship multiple sclerosis drug, Avonex.

The shares of Biogen, which has a market capitalization of roughly $19.3 billion, rose more than 16 percent to $81.59 in after-hours trading, following the Friday announcement.

The stock of the Cambridge, Massachusetts-based company closed up 3.4 percent at $69.43 in regular trade, the highest since late 2001. Biogen's shares gained more than 35 percent this year.

The move follows biotech company MedImmune's agreement earlier this year to be acquired by Anglo-Swedish drugs group AstraZeneca Plc (AZN.L: Quote, Profile, Research, Stock Buzz) for more than $15 billion in the industry's biggest deal this year.

"There has been a lot of speculation during the last six months -- since MedImmune was acquired," said Eric Schmidt, an analyst at Cowen & Co.

Applying a MedImmune-type earnings multiple to Biogen could mean a take-out price of $200 a share, Schmidt said, adding he does not think Biogen will get that much.

Analysts said possible suitors could include big drug companies, which are desperate to fill their product pipelines and have ample cash to spend on acquisitions.

The announcement comes four years after Biogen was acquired by Idec Pharmaceutical Corp for $6.7 billion.