California-based biotech Amgen amgn on Wednesday notched an important victory over rival drugmakers Sanofi and Regeneron regn as a jury ruled that two of its patents on a major new cholesterol drug are valid.

The dispute centers on two relatively new cholesterol-fighting medications from the firms: Amgen’s Repatha and Sanofi/Regeneron’s Praluent. And the jury’s decision was met with immediate pushback from Amgen’s allied competitors, who said they will appeal the decision.

“[T]his decision is the first step in this ongoing litigation and does not impact Praluent (alirocumab) Injection or our ability to deliver it to physicians and patients at this time,” wrote the companies in a statement.

The so-called PCSK9-inhibitors were approved in the U.S. on each other’s heels last year and are expected to eventually become major blockbusters with multi-billion dollar market potential thanks to their formidable cholesterol-lowering ability—even though initial uptake hasn’t been mind-blowing.

Practically speaking, the jury’s decision throws a wrench into Sanofi and Regeneron’s claims that Amgen’s patents on Amgen’s PCSK9-targeting antibodies are too broad to be viable. Barring a reversal, there’s a chance that the former companies will have to pay competitor Amgen royalties in order to sell their own therapy in the U.S.

Sanofi has already been forced to reckon with drug competition in flagship therapeutic portfolios such as diabetes with the advent of biosimilars, or generic alternative to biologic drugs like insulin, and rivals like Novo Nordisk nvo and Eli Lilly lly .