Another day, another biotech acquisition for drugmaker Genzyme (NASDAQ:GENZ). Following on the heels of its $580 million buyout of AnorMED near the end of last year, Genzyme announced it was acquiring partner Bioenvision (NASDAQ:BIVN).

Bioenvision and Genzyme have been partnered together on the leukemia drug Clolar; Genzyme markets the drug in the U.S., and Bioenvision markets it in the EU. Currently the compound has a very narrow label that has inhibited sales. Clinical studies and marketing applications are underway to widen the compound's label and expand its use into more lucrative indications like solid tumors.

The $345 million all-cash buyout values Bioenvision at $5.60 a share, barely more than a 6% premium to what shares were trading at before yesterday. It's a little suspicious to me how the shares have traded over the past two weeks. They are up nearly 70% since May 14 on no news at all -- but that's something for the regulators to possibly sort out.

The buyout offer is a sign of Genzyme's confidence in Clolar gaining an improved label since Bioenvision has no meaningful product pipeline besides the Clolar label-expanding studies. With the acquisition, Genzyme will get complete control of Clolar and not have to pay royalties on future sales of the drug, so perhaps something in the Clolar data is giving Genzyme confidence in the drug.

With more than $500 million in free cash flow last year alone, Genzyme has money to spare. Since it has chosen to forgo the dividend route, acquisitions and stock buybacks (such as the one it initiated yesterday that could reach $1.5 billion in value) make sense. And the Bioenvision acquisition is a relatively lower-risk buyout considering that Clolar is a proven drug already approved in the U.S. and EU.

Looking for more Foolish drug stock coverage? Check out the Fool's market-beating Rule Breakers newsletter. You can check out all our recommendations as well as get access to our message boards and exclusive content with a 30-day free trial.

Fool contributor Brian Lawler does not own shares of any company mentioned in this article. The Fool has a disclosure policy.