Arcus Kidney Cancer Drug Casdatifan Progresses to Rival Merck’s Welireg

Arcus Biosciences is advancing its position in the competitive field of kidney cancer treatment with promising results from its current research. The biotech company is focusing on casdatifan, a HIF-2a inhibitor, as a potential rival to Merck's FDA-approved drug, Welireg, which treats advanced renal cell carcinoma. Recently, at the 2025 American Society of Clinical Oncology (ASCO) Annual Meeting, Arcus presented updated data from its Phase I/Ib trial that highlighted the potential of casdatifan.

The initial abstracts released for the conference noted a 41% response rate in patients treated with casdatifan. By the time of the oral presentation, this rate had increased to 46%, indicating one complete response and ten partial responses among 24 patients with metastatic kidney cancer. These patients had previously been treated with, and progressed on, immunotherapy.

Arcus administered casdatifan in conjunction with Exelixis’ Cabometyx. According to the company, there were meaningful overlapping toxicities between the two drugs, but no Grade 4 or 5 adverse events were attributed to casdatifan. Truist Securities analysts reacted positively, noting that the improved response rate aligns with their expectations based on Merck's Welireg data. Welireg, like casdatifan, targets the protein that facilitates tumor growth by promoting new blood vessel formation.

Merck's Welireg showed a response rate of 32% and a median progression-free survival (PFS) of 13.8 months in similar studies. While Arcus has yet to release survival data from its Phase I/Ib trial, they have observed patients for a median of 5.3 months. The biotech plans to initiate a Phase III trial, focusing on kidney cancer patients who have received prior anti-PD-1/L1 immunotherapy. Arcus's trial will use progression-free survival as the primary endpoint, with overall survival as a significant secondary endpoint.

Earlier this year, Gilead decided against licensing casdatifan, leading Arcus to organize a stock offering to support its development efforts, with Gilead participating. As of March, Arcus reported having $1 billion in assets, a reserve meant to sustain operations beyond the initial results of the forthcoming Phase III trial. At the same time, Arcus carried a debt of $1.2 billion.

With these developments, Arcus is positioning itself as a competitor in the kidney cancer treatment market, particularly against Merck. The upcoming trials will be critical in determining casdatifan's viability as a treatment option, hoping to match or exceed Merck's established benchmarks with Welireg. The biotech's strategic moves and financial maneuvers indicate a commitment to expanding its footprint in the oncology field, with casdatifan at the forefront of its efforts.