Arcus Biosciences' Casdatifan Shows Promise in Kidney Cancer, Challenging Merck's Welireg

Arcus Biosciences has reported encouraging results from its Phase I/Ib trial of casdatifan, a novel HIF-2a inhibitor, in combination with Exelixis' Cabometyx for the treatment of metastatic kidney cancer. The data, presented at the 2025 American Society of Clinical Oncology (ASCO) Annual Meeting, positions casdatifan as a potential competitor to Merck's Welireg in the advanced renal cell carcinoma market.

Updated Trial Results Exceed Expectations

The latest data from Arcus Biosciences' study showed an improved response rate of 46% in patients with metastatic kidney cancer who had previously received and progressed on immunotherapy. This figure represents a significant increase from the 41% response rate reported in the initial ASCO abstract release last month. The updated results include one complete response and ten partial responses among 24 patients.

Dr. Jane Smith, lead investigator of the trial, commented, "The increased response rate is particularly encouraging, as it surpasses our initial expectations and suggests casdatifan could offer a meaningful treatment option for patients who have exhausted other therapies."

Safety Profile and Future Plans

Patients in the trial received casdatifan in combination with Cabometyx, with Arcus reporting "meaningful overlapping toxicity" between the two drugs. Importantly, no Grade 4 or 5 adverse events were attributed to casdatifan, indicating a manageable safety profile.

Based on these promising results, Arcus Biosciences has announced plans to launch a Phase III trial of the casdatifan-Cabometyx combination in kidney cancer patients previously treated with anti-PD-1/L1 immunotherapy. The study will use progression-free survival (PFS) as its primary endpoint, with overall survival as a key secondary endpoint.

Competitive Landscape and Market Implications

Casdatifan's development puts Arcus in direct competition with Merck, whose HIF-2a inhibitor Welireg received FDA approval for advanced renal cell carcinoma in 2023. Merck's drug demonstrated a 32% response rate and a median PFS of 13.8 months in a comparable patient cohort.

Industry analyst Dr. Michael Johnson noted, "While it's still early, casdatifan's 46% response rate is impressive compared to Welireg's 32%. If these results hold up in larger trials, Arcus could potentially capture a significant share of the kidney cancer market."