Biogen Future in Flux as CEO Exits: BioBuzz

Either way, the search for a new Biogen CEO, which the company said is already underway, will be an interesting process to watch. Now that Mullen is essentially a lame duck, it's reasonable to expect the company's board -- including Icahn's proxies -- to take a more active management role.

Naturally, speculation will increase that Biogen could be placed back on the sale block.

It might be lost amidst all the palace intrigue, but Mullen did manage to bring home a 12% return for shareholders in 2009 -- making Biogen the only big-cap biotech stock to close the year in the green.

Still, Biogen does face challenges ahead with the increase in the number of cases of the serious brain infection known as PML tied to use of its multiple sclerosis drug Tysabri. The company has also experienced setbacks recently with its late-stage drug pipeline.

Biogen shares closed Monday at $53.64, ahead of the announcement of Mullen's retirement.

Help Wanted: Big-Cap Biotech CEO

Running a multi-billion dollar, profitable biotech firm isn't a position that comes available very often, which makes the search for a new CEO at Biogen Idec a relatively rare event.

Mullen joined Biogen in 1989 and rose to the CEO post in 2000, the same year that Amgen's(AMGN) current CEO Kevin Sharer also took over the top job at his company.

Genzyme's(GENZ) CEO Henri Termeer is the longest-serving CEO in the big-cap biotech group, named to the position in 1985. [How long he stays there is also an intriguing question for 2010.]

John Martin became Gilead Sciences(GILD) CEO in 1996, while Celgene(CELG) CEO Sol Barer is a relative newcomer, having been promoted to his position in 2006. [Although Barer's tenure with Celgene began in 1987.]