Arcus Biosciences reported Nature-published ARC-20 findings showing investigational HIF-2α inhibitor casdatifan achieved durable responses in metastatic clear cell renal cell carcinoma, with serum EPO suppression emerging as a biomarker linked to improved progression-free survival.
Written By: Farha Farheen, PharmD
Reviewed By: Pharmacally Editorial Team
Arcus Biosciences has reported new translational and clinical findings showing that treatment with the investigational HIF-2α inhibitor casdatifan (AB521) produced deep and sustained suppression of serum erythropoietin (EPO), a biomarker that closely tracked with improved clinical outcomes in patients with metastatic clear cell renal cell carcinoma (ccRCC). Published in Nature, the research represents the first comprehensive analysis linking HIF-2α inhibition, circulating EPO changes, tumor biology, and patient outcomes in advanced kidney cancer.
The publication combines biomarker analyses with efficacy data from multiple monotherapy cohorts of the ongoing ARC-20 platform study (NCT05536141). Investigators found that patients whose tumors showed high HIF-2α activity and experienced greater reductions in serum EPO achieved higher objective response rates and longer progression-free survival (PFS), providing biological evidence that effective HIF-2α blockade translates into meaningful clinical benefit.
Biomarker Findings Reinforce HIF-2α Inhibition Strategy
Clear cell renal cell carcinoma is the most common form of kidney cancer and is frequently driven by abnormal activation of the hypoxia-inducible factor 2-alpha (HIF-2α) pathway. This transcription factor regulates hundreds of genes involved in tumor growth, angiogenesis, and adaptation to low-oxygen environments. Casdatifan is an oral small-molecule inhibitor developed to provide sustained suppression of this pathway.
The study showed that serum EPO, a downstream product of HIF-2α signaling, consistently reflected target inhibition during treatment. Patients with deeper and more durable EPO suppression experienced better clinical outcomes, while higher baseline HIF-2α pathway activity and tumor EPO expression also correlated with improved responses. Together, these findings support serum EPO as a practical pharmacodynamic biomarker for monitoring HIF-2α inhibition and identifying patients most likely to benefit from therapy.
ARC-20 Study Demonstrated Durable Clinical Activity
The analysis included four casdatifan monotherapy cohorts involving 121 patients with metastatic ccRCC who had received extensive prior treatment, including immune checkpoint inhibitors and VEGFR tyrosine kinase inhibitors. More than half had undergone at least three previous lines of therapy, while 71% had intermediate or poor International Metastatic Renal Cell Carcinoma Database Consortium (IMDC) risk.
At the August 15, 2025, data cutoff, pooled results showed a confirmed objective response rate (cORR) of 31% and a median progression-free survival of 12.2 months. In the 100 mg once-daily tablet cohort, which represents the dose being evaluated in the ongoing Phase 3 PEAK-1 study (NCT07011719), the confirmed objective response rate reached 35%, while median PFS had not yet been reached and 60% of patients remained progression-free at 12 months. A subsequent analysis with a January 30, 2026 data cutoff extended median PFS in this cohort to 15.1 months.
Casdatifan maintained a manageable safety profile across dose groups. The most common treatment-related Grade 3 or higher adverse events were anemia and hypoxia, consistent with the HIF-2α inhibitor class. No patients discontinued treatment because of anemia, and only 2% discontinued because of hypoxia, with no unexpected safety signals reported.
Publication Supports Ongoing Phase 3 Development
Lead investigator Toni K. Choueiri, MD, said the study is the first to comprehensively connect HIF-2α-associated EPO suppression with tumor biology and clinical outcomes, noting that patients achieved progression-free survival exceeding one year despite extensive prior treatment.
Arcus Chief Medical Officer Richard Markus, MD, PhD, said the translational findings validate serum EPO as a biomarker of HIF-2α inhibition and reinforce the company’s confidence in casdatifan’s clinical potential.
Arcus is advancing casdatifan across multiple treatment settings, including first-line combination regimens and second-line therapy with cabozantinib. The global PEAK-1 Phase 3 trial is currently enrolling patients with metastatic ccRCC, and the company expects to complete enrollment and initiate an additional first-line Phase 3 study by the end of 2026. Casdatifan remains an investigational therapy and has not yet received regulatory approval.
What This Means for Patients
Researchers found that casdatifan, an experimental oral medicine for advanced kidney cancer, helped slow disease progression in many patients whose cancer had already stopped responding to several previous treatments. The study also showed that a simple blood marker called erythropoietin (EPO) may help doctors determine how well the treatment is working. While these findings are encouraging, casdatifan is still being tested in Phase 3 clinical trials and has not yet been approved for routine use. Further studies will confirm its safety and effectiveness before it becomes widely available.
About the Writer
Farha Farheen, PharmD (LinkedIn) is a pharmacy professional with a strong interest in pharmacovigilance and clinical research. She has completed her Doctor of Pharmacy (Pharm.D) along with her internship as a Clinical Pharmacist. She has hands-on experience in adverse drug reaction (ADR) reporting, safety data documentation, and pharmacovigilance workflows, and is proficient in using VigiFlow. She is also a patent holder for an antibacterial formulation enriched with bioactive substances, granted by the German Patent and Trademark Office.