Written by Tracy Staton

Sanofi S A (NYSE: SNY ) is in talks to buy Flexion Therapeutics, Inc. (Nasdaq: FLXN), a Boston-area biotech with its lead product now awaiting FDA approval, for more than $1 billion in cash.

Flexion’s board has accepted Sanofi’s non-binding offer, with a price in the “mid-30s” per share, the source said, with a final price pending due diligence according to a source close to the deal. Flexion stock closed Wednesday at $19.68. Sanofi refused to comment on the potential deal. Flexion spokesman Scott Young said he “can’t comment on market speculation or rumors.”

The talks are ongoing and the transaction may not come to fruition, the source said but if due diligence goes well and a binding offer is accepted, the cash deal could close quickly, giving Sanofi’s Genzyme unit several months to gear up for the Zilretta launch.

Flexion’s knee injection for osteoarthritis, Zilretta, would fit right in with Sanofi’s biosurgery division, which markets its own osteoarthritis injectable, Synvisc and some of Flexion’s staffers know that product well; marketing VP Mark Fraga and medical affairs VP Scott Kelley, M.D., jumped to Flexion last year from jobs handling Synvisc at Sanofi.,,

Zilretta is a sustained-release corticosteroid first up for approval for use in the knee. Analysts have suggested it could bring in $500 million to $600 million in peak sales, and perhaps hit blockbuster status if it wins indications for use in other joints.

Synvisc works differently; it’s a hyaluronon-based injection designed to supplement the natural fluid in the knee. It brought in €408 million for Sanofi in 2016, with €313 million of that in the U.S.

Sanofi has been deal-shopping as its diabetes franchise slows, eyeing companies with price tags in the bolt-on range—as Flexion would be—as well as bigger targets. It’s had some trouble bringing those bigger deals across the finish line, however; it lost out to Pfizer Inc. (NYSE: PFE) on the cancer biotech Medivation last summer and to Johnson & Johnson (NYSE: JNJ) in its attempt to snap up Swiss-based Actelion Ltd. (PINK:ALIOF) late last year.