Background: In KEYNOTE-426, pembro + axi significantly improved OS (HR 0.53, P < .0001), PFS (HR 0.69, P = .0001), and ORR (59.3% vs 35.7%, P < .0001) vs sunitinib and had manageable toxicity as first-line therapy for mRCC (NCT02853331). The pembro + axi benefit was observed across all IMDC risk groups and regardless of PD-L1 expression. We present data for the combined intermediate/poor risk group and for patients (pts) with sarcomatoid features. Methods: 861 eligible pts with clear-cell mRCC, no prior systemic therapy for mRCC, and KPS ≥70 were randomized 1:1 to pembro 200 mg IV Q3W for a maximum of 35 cycles plus axi 5 mg orally BID (N = 432) or sunitinib 50 mg orally QD (4-wk on/2-wk off) (N = 429). Primary endpoints were OS and PFS (RECIST v1.1 by blinded, independent central review [BICR]). ORR (RECIST v1.1 by BICR) was the key secondary endpoint. The intermediate/poor risk group was prespecified; the sarcomatoid group was exploratory. HRs and their 95% CIs were calculated with a Cox proportional hazards model. None of the analyses were multiplicity-controlled. Results: 592 (68.8%) of all randomized pts were of IMDC intermediate/poor risk — 294 in the pembro + axi arm, 298 in the sunitinib arm. Pembro + axi improved OS (HR 0.52, 95% CI 0.37-0.74; 12-mo rate 87.3% vs 71.3%), PFS (HR 0.67, 95% CI 0.53-0.85; median 12.6 vs 8.2 mo), and ORR (55.8% [95% CI 49.9-61.5] vs 29.5% [24.4-35.1]) in pts with intermediate/poor risk; CR rates were 4.8% (95% CI 2.6-7.9) vs 0.7% (0.1-2.4). Of the 578 pts with known status, 105 (18.2%) had sarcomatoid features — 51 in the pembro + axi arm, 54 in the sunitinib arm. Pembro + axi improved OS (HR 0.58, 95% CI 0.21-1.59; 12-mo rate 83.4% vs 79.5%), PFS (HR 0.54, 95% CI 0.29-1.00; median not reached vs 8.4 mo), and ORR (58.8% [95% CI 44.2-72.4] vs 31.5% [19.5-45.6]) in pts with sarcomatoid features; CR rates were 11.8% (95% CI 4.4-23.9) vs 0% (0.0-6.6). Conclusions: Pembro + axi provides benefit in the combined population of pts with IMDC intermediate or poor risk and in pts whose tumors had sarcomatoid features. The observed benefits were consistent with those seen in the total population. Clinical trial information: NCT02853331