It has to be a little disheartening for a CEO to announce his retirement and see shares of the company's stock open up 2%, but such is the life of Biogen Idec's (NASDAQ:BIIB) James Mullen.

In addition to small-fry investors, I imagine Carl Icahn is smiling a little, too. You'll recall that Icahn launched two attempts to board the M.S. Biogen, with the second ending in a pair of board seats for his slate of nominees.

Investors are justified to be upset with Mullen's performance of late, especially compared with some of the company's drug-making brethren.

Company

Market Cap (in Billions)

Share Increase
Over Past 3 Years

Biogen Idec

$15.5

13.4%

Gilead Sciences (NASDAQ:GILD)

$39.0

64.7%

Celgene (NASDAQ:CELG)

$25.6

72.0%

Bristol-Myers Squibb (NYSE:BMY)

$49.9

(4.37%)

Source: Google Finance.

But Mullen's nearly decade-long tenure as CEO hasn't been all bad. He oversaw the merger with Idec Pharmaceuticals, which brought in Rituxan and the approval and reapproval of Tysabri, which it markets with Elan (NYSE:ELN). Most recently, the company managed to remove part of a deal between Elan and Johnson & Johnson (NYSE:JNJ) that might have reduced Biogen's value as a takeover target.

To get Biogen's shares out of their funk, Mullen's successor will need to increase revenue of both its current offerings as well as new ones. There's potential for Tysabri sales to accelerate again if Elan and Biogen can get the progressive multifocal leukoencephalopathy (PML) side effect to a reasonable level. It also has quite a few drugs in the pipeline, including Acorda Therapeutics' (NASDAQ:ACOR) Fampridine-SR, to which Biogen licensed the rights excluding the U.S.

And of course, there's still the possibility of orchestrating a sale of the company, although the issues from the first attempted sale still remain. Keep your head up, Mullen; I'm not sure your successor will be able to do much better.

Is Mullen's departure a good thing for the company or a minor milestone in the company's timeline? Let us know in the comments box below.