Court of Appeal upholds enzalutamide patent validity in Accord Healthcare dispute

The Court of Appeal (Civil Division) dismissed an appeal in Accord Healthcare Limited & Ors v The Regents of the University of California & Anor on 23rd July 2025, upholding the validity of European Patent (UK) No. 1 893 196 and Supplementary Protection Certificate (SPC) No. SPC/GB13/079 covering enzalutamide, a treatment for hormone-refractory prostate cancer.

The appellants had challenged Mr Justice Mellor's earlier judgement of 7 November 2024, which rejected their revocation claims based on alleged obviousness over prior art. The dispute centred on whether the patent's inventiveness claims could withstand scrutiny against two key pieces of prior art: "the Poster" and "the Slides," which detailed similar antiandrogen compounds for prostate cancer treatment.

Prior art and obviousness analysis

The appellants argued that enzalutamide's structural formulation represented an obvious development from the referenced prior art, which had already demonstrated compounds with comparable therapeutic properties. The Court examined whether a hypothetical "skilled team" comprising a cancer biologist and medicinal chemist would have considered the modifications leading to enzalutamide as predictable rather than inventive.

Expert witnesses presented contrasting interpretations of the prior art's significance. Whilst the Poster and Slides had contributed meaningfully to understanding antagonistic activity against the androgen receptor, the Court determined that this knowledge did not render enzalutamide's development obvious to the skilled addressee.

Judicial reasoning and precedent

Lord Justice Arnold, leading the three-judge panel alongside Lord Justice Snowden and Lord Justice Zacaroli, emphasised the robustness of the original adjudication. The Court applied established legal principles governing obviousness assessments, drawing upon precedents that recognise the multifaceted nature of invention evaluations in pharmaceutical patents.

The judgement highlighted the substantial evidential burden required to establish obviousness in patent law. The Court found that whilst the appellants' arguments possessed some technical merit, they failed to demonstrate convincingly that the claimed invention lacked the requisite inventive step.

Technical considerations

The assessment required careful evaluation of how the skilled team would have approached the development of improved antiandrogen therapies. The Court considered whether the modifications distinguishing enzalutamide from the prior art compounds would have been obvious developments or represented genuine inventive advances warranting patent protection.

Expert testimony revealed competing interpretations of the technical landscape at the priority date. However, the Court concluded that the evidence did not support the proposition that enzalutamide's particular structural features and therapeutic advantages would have been apparent to skilled practitioners working in the field.

Implications

The decision reinforces the high threshold required for successful obviousness challenges in pharmaceutical patents. The Court's analysis demonstrates the careful balance between recognising incremental scientific progress and maintaining appropriate standards for patentability in medical innovation.

The judgement also underscores the importance of comprehensive expert evidence in patent disputes, particularly where technical assessments require interdisciplinary expertise spanning both biological and chemical domains.

The dismissal of the appeal provides continued protection for the enzalutamide patent, affirming that pharmaceutical innovators can maintain exclusivity over compounds that demonstrate genuine inventive merit, even where prior art reveals related therapeutic approaches. This outcome supports the pharmaceutical industry's investment in developing novel treatments whilst maintaining rigorous standards for patent validity.