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Safety and differential clinical activity of nivolumab plus ipilimumab (nivo-ipi) in patients (pts) with non-clear cell renal cell carcinoma (nccRCC).

356 Background: Pembrolizumab monotherapy recently showed promising efficacy in nccRCC. The objective response rate (ORR) by histology was 28.8% for papillary, 9.5% for chromophobe, and 30.8% for unclassified RCC (McDermott, JCO 2021). However, combination immunotherapy data are limited in nccRCC. Methods: We retrospectively evaluated the efficacy and safety of nivo-ipi in pts with nccRCC treated at our institution. ORR and progression-free survival (PFS) were determined using RECIST. Overall survival (OS) was measured from therapy start to death or last follow up. Results: Between November 2017 and July 2020, 27 pts with nccRCC were treated with nivo-ipi at our institution; 25 pts (93%) received nivo-ipi as first-line therapy and 14 pts (52%) had prior nephrectomy. Histology subtypes included 13 (48%) papillary (4 with sarcomatoid features [SF]), 7 (26%) chromophobe (4 with SF), and 7 (26%) unclassified. Sites of metastases included lung in 52%, bone in 37%, and liver in 22% of pts. IMDC risk was favorable (8%), intermediate (48%) and poor (44%). ORR in all pts was 30%; 7 pts achieved a partial response (PR), and 1 patient achieved a complete response (CR). ORR by histology subtype was 54% for papillary, 14% for chromophobe, and 0% for unclassified (table). Clinical benefit (defined as PR, CR, or stable disease [SD] for > 6 months) was achieved in 62% for papillary, 57% for chromophobe, and 29% for unclassified. At a median follow-up time of 17.1 months, for all 27 pts, median PFS was 7.2 months, and median OS was 18.5 months. Median OS per each variant histology subtype was not reached in papillary, 25.7 months in chromophobe, and 7.4 months in unclassified. Median PFS per variant histology subtype was 11.8 months in papillary, 4.0 months in chromophobe, and 2.8 months in unclassified. Seven pts (26%) developed Grade ≥3 toxicity: pneumonitis (2), colitis (2), hepatitis (1), rash (1), and immune-mediated glomerulonephritis (1). Conclusions: In this small retrospective study, nivo-ipi was well-tolerated in pts with nccRCC and yielded high ORR and prolonged PFS in papillary RCC but disappointing efficacy results in chromophobe and unclassified RCC. Molecular studies are ongoing to understand the mechanisms of response and resistance to nivo-ipi in these tumor subtypes.[Table: see text]