(Adds details on Icahn offer)
BOSTON, Oct. 12 (Reuters) - Biogen (BIIB.O) (BIIB.O) Idec Inc (BIIB.O), 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) 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.
The company said it hired Goldman Sachs & Co and Merrill Lynch & Co to help find a buyer and that it has already received "expressions of interest."
One interested party, Biogen said, is billionaire investor Carl Icahn, who recently took control of biotechnology company ImClone Systems Inc IMCL.O.
Icahn, who has increased his stake in Biogen to about 4 percent from 1 percent, last week made an offer for the company of at least $23 billion, the Wall Street Journal reported, citing people familiar with the matter.
"Potential suitors will likely be the big pharmaceuticals companies, as well as those that already have partnerships with Biogen," said Damien Conover, an analyst at Morningstar.
Incorporated in 1978, Biogen is one of the most established names in the biotech industry, with products to treat multiple sclerosis, cancer and arthritis.
Biogen's best-selling product, Avonex, posted an 8 percent jump in revenue to $462 million in the June-ending quarter, with the bulk of the growth coming from overseas.
The drug was the main driver behind Biogen Idec's 17 percent jump in quarterly revenue to to $773 million.
The company's other multiple sclerosis drug, Tysabri, is rebounding after being pulled from the market in 2005 due to safety concerns. Biogen said in July that physician adoption of the drug is progressing steadily.
And just this week, Biogen and its marketing partner Elan Corp ELN.N said there have been no new cases of a potentially deadly brain infection in patients taking the drug.
Biogen and partner Genentech Inc DNA.N market Rituxan, a drug approved to treat non-Hodgkin's lymphoma and rheumatoid arthritis. Quarterly sales rose 12 percent to $231 million in the June-ending period.
The strong returns in July led Biogen to raise its revenue growth target to 16-18 percent in 2007 from an earlier view of growth in the "mid-teens." (Reporting by Toni Clarke, Deena Beasley, Svea Herbst, Jessica Hall, and Chris Reiter)