The 30-second summary
Design: Phase 1 (ARC-20), casdatifan (AB521) monotherapy and combinations in advanced clear cell RCC. Key readout: durable clinical activity in heavily pretreated patients, published in Nature. Regulatory: investigational — NOT FDA approved (belzutifan/Welireg is the approved HIF-2α inhibitor in RCC). Sponsor / drug: Arcus Biosciences; casdatifan (AB521, oral HIF-2α inhibitor).
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📊 @DrRanaMcKay presents pooled safety of casdatifan monotherapy from ARC-20 at #KCRS26 🔬 💊 Dose expansion in 2L+ metastatic ccRCC, HIF-2α inhibitor naive, pooled N=127 across 50 mg BID, 50 mg QD, 100 mg QD and 150 mg QD, median treatment duration 9.7 months 🩸 Treatment related anemia in 89% pooled and 84% at the 100 mg QD phase 3 dose, grade 3 or higher in 40% and 25% 🫁 Hypoxia in 16% and 13%, the other on target effect of HIF-2α inhibition ⚖️ Treatment related grade 3 or higher AEs in 49% pooled and 38% at the phase 3 dose, managed largely with dose modification: reduction in 24% and 22%, discontinuation in only 3% and 3% ⚠️ No grade 5 treatment related AEs 🧬 ESA use did not appear to negatively impact rPFS @kidneycan
Overview
ARC-20 is a Phase 1 study of casdatifan (AB521), an oral hypoxia-inducible factor-2 alpha (HIF-2α) inhibitor from Arcus Biosciences, evaluated as monotherapy and in combination regimens in advanced clear cell renal cell carcinoma. Results published in Nature in 2026 showed durable clinical activity in heavily pretreated patients alongside biomarker correlates of HIF-2α engagement. Casdatifan is investigational and remains under active clinical development, including a Phase 3 program.
Primary endpoint — Efficacy (Phase 1)
In ARC-20, casdatifan demonstrated durable clinical activity in heavily pretreated advanced clear cell RCC, with results published in Nature. Response and duration figures, together with biomarker correlates of HIF-2α inhibition, were highlighted by KOLs in the posts above and detailed in the primary publication.
Durable activity in heavily pretreated ccRCC (Nature)Safety
KOLs described a manageable safety profile consistent with HIF-2α inhibition, whose class-defining adverse events include anemia and hypoxia. See the KOL posts and the Nature publication for the detailed safety data.
Clinical implications
⚠️ Investigational — casdatifan (AB521) is NOT FDA approved. ARC-20 Phase 1 data support continued development as a next-generation HIF-2α inhibitor in clear cell RCC. Belzutifan (Welireg) is the currently FDA-approved HIF-2α inhibitor in this space (advanced and, as of June 2026, adjuvant RCC).