Sanofi-Aventis just boosted its stake in Regeneron Pharmaceuticals to 19 percent and expanded its collaboration into cancer research as part of the deal to include arthritis and other maladies. The deal, which includes an upfront payment of $85 million and up to $475 million tied to research, could reach as much as $872 million, according to a statement.

Marc Cluzel, head of research at the French drugmaker, last month indicated Sanofi wants to acquire products from other companies to push more biotech meds to the market, Bloomberg News notes. Sanofi, set to lose patent protection on products that generated almost half of last year’s sales by the end of 2012, needs new drugs to replace some of its biggest sellers as well as the failure of its Acomplia diet pill to pass muster in the US.

“From a strategic point of view, it makes sense because obviously it’s a company they know already, so that makes it a little less risky,” Denise Anderson, an analyst at Kepler Landesbanki in Zurich, tells Bloomberg. “The terms are very favorable for Regeneron. It certainly shows who has the power these days: the biotechnology companies.”

How so? Sanofi, which held 4 percent of Regeneron before the announcement, is paying 52 percent more than yesterday’s $17.15 closing price.

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