The investment community has been willing Biogen to make a big deal for some time now but a modest pact inked with Japan's TMS for its Phase II acute ischemic stroke drug suggests that management will continue to favor picking up promising compounds rather than diving into major M&A.

Sales of Biogen's blockbuster rare disease drug moderated in the first quarter as the company worked through the bolus of urgent infant and pediatric patients awaiting treatment in the US.

Biogen's MS therapy natalizumab may have been a disappointment in ischemic stroke, but the neuroscience-focused company is aiming to soon move another potential stroke therapy into late-stage clinical studies.

The firm announced a small deal with Karyopharm for a preclinical asset with potential in ALS, but large deals are also being considered, management told the fourth quarter earnings call.