Amgen v Sanofi: EPO appeal withdrawal confirms European alignment

Further to our recent article discussing the global dispute between Sanofi/Regeneron and Amgen over the validity of patents covering therapeutic antibodies against PCSK9, a significant development has now brought the EPO proceedings to a close. The opponents have withdrawn their appeals in respect of EP 3 666 797, Amgen’s patent directed to anti‑PCSK9 antibodies for medical use. As a result, the EPO Opposition Division’s decision upholding the patent as granted is now final.

This marks an important consolidation of the European position following the Court of Appeal’s decision in the parallel UPC proceedings in late 2025, which also confirmed the validity of the same patent. Together, these outcomes signal a clear alignment between the EPO and UPC in their assessment of antibody and medical use claims.

Final confirmation of inventive step at the EPO

The EPO’s reasoning, now unchallenged, reinforces a key principle highlighted in earlier stages of the dispute: when assessing inventive step for medical use claims, the decisive question is not simply whether the prior art motivates the skilled person to pursue a given therapeutic target, but whether it provides a reasonable expectation that the claimed treatment will be effective.

In the case of PCSK9, although the prior art suggested targeting the protein, it left open fundamental uncertainties about its biological mechanism and therapeutic relevance. The EPO had therefore concluded that the skilled person would not have expected, with any degree of confidence, that antibodies blocking PCSK9 would successfully treat hypercholesterolaemia. That conclusion now stands as the final word in the EPO proceedings.

Alignment with the UPC

The withdrawal of the appeal is particularly notable in light of the earlier divergence between the EPO and the UPC at first instance. While the UPC Central Division initially revoked the patent as obvious, the UPC Court of Appeal reversed that decision, placing emphasis, like the EPO, on the absence of a reasonable expectation of therapeutic success.

With both tribunals now reaching the same outcome, this case represents one of the clearest early examples of substantive convergence between the EPO and UPC. Although differences in analytical framework remain, the underlying approach to inventive step in life sciences cases appears increasingly consistent.

Practical implications

For patentees, the outcome reinforces that in Europe, functional antibody claims, particularly in medical use form, remain robust where they are grounded in a genuine and non-obvious therapeutic contribution.

More broadly, the case highlights a now well-established transatlantic divide; while the US Supreme Court has imposed strict constraints on broad antibody claims through enablement, Europe continues to assess such inventions primarily through the lens of inventive step, with “reasonable expectation of success” as a central test.

Conclusion

The closure of the EPO appeal proceedings brings welcome certainty to a long-running dispute and a growing alignment between the EPO and UPC; an important development for the future of biotechnology patent litigation in the region.