First-Line Pembrolizumab (Pembro) Monotherapy For Advanced Non-Clear Cell Renal Cell Carcinoma (Nccrcc): Results From Keynote-427 Cohort B.

546Background: PD-1/L1 pathway inhibitors are effective in clear cell (cc)RCC, but efficacy of PD-1 inhibitors (or any therapy) in nccRCC has not been established. KEYNOTE-427 is a single-arm, open-label, phase 2 study of pembro monotherapy in patients (pts) with advanced ccRCC (cohort A) and nccRCC (cohort B). Cohort B results are presented. Methods: 165 pts with histologically confirmed nccRCC, no prior systemic therapy, measurable disease (RECIST v1.1), and KPS ≥70% enrolled. Pts received pembro 200 mg IV Q3W for 35 cycles (~2 y) or until progressive disease (PD), unacceptable toxicity, or withdrawal. Pts were followed after PD for overall survival. Primary end point: objective response rate (ORR) per RECIST v1.1 by blinded independent central review. Secondary end points included duration of response (DOR) and population description by International Metastatic RCC Database Consortium (IMDC) risk. Exploratory end points: ORR by histology and PD-L1 expression (combined positive score [CPS] ≥1 for PD-L1+...