Background: Identification of effective systemic therapy for non-clear cell renal cell carcinoma (RCC) remains a unmet need. We reported a two arm, phase 2 trial of cabozantinib plus nivolumab (CaboNivo) that showed promising efficacy in the treatment arm comprised primarily of papillary and unclassified histology. (Lee, JCO, 40: 2022). Herein, we report updated results with extended follow up. Methods: Patients had advanced non-clear cell RCC, 0 or 1 prior systemic therapies excluding prior immune checkpoint inhibitors, and measurable disease by RECIST. Cabo 40 mg/day plus Nivo 240 mg every 2 weeks or 480 mg every 4 weeks was given for both arms. Arm 1 was comprised of papillary, unclassified, or translocation associated RCC; and Arm 2 had chromophobe RCC (closed early for lack of efficacy). The primary endpoint was objective response rate (ORR) by RECIST; secondary endpoints included progression-free survival (PFS), overall survival (OS), duration of response (DOR) and safety. Arm 1 was a single stage design that met its primary endpoint and was expanded to produce more precise estimates of ORR. Correlative analyses by next generation sequencing were performed and will be presented. Results: A total of 40 patients were treated in Arm 1 (data cutoff: Dec 13, 2022). Median follow up time was 34 months (range 20, 51). Twenty-six patients (65%) were previously untreated, and 14 (35%) had 1 prior treatment line: 10 (25%) received prior VEGF-targeted therapy and 8 (20%) received prior mTOR-targeted therapy. ORR is 48% (95% CI 31.5–63.9). Median PFS is 13 months (95% CI: 7, 16). Progression-free survival is 51% (95% CI: 34, 65) at 12 months and 23% (95% CI: 11, 37) at 24 months. Median OS is 28 months (95% CI: 23, 43). Overall survival is 70% (95% CI: 53, 82) at 18 months and 44% (95% CI: 28, 60) at 36 months. PFS and OS were similar for previously treated and untreated patients. For responders, median DOR was 17 months (95% CI: 10, 36). Adverse effects of any grade were experienced by 35 patients (88%); grade 3/4 adverse events were experienced by 22 patients (55%). Grade 3/4 AST and ALT elevations were 18% and 23% respectively. Other common grade 3/4 adverse events were hypertension (5, 13%) and pain (4, 10%). Study therapy was discontinued in 9 patients (28%) for toxicity. Conclusions: Updated results with extended follow-up highlight efficacy and safety for CaboNivo in metastatic non-clear cell RCC pts with papillary, unclassified, or translocation associated histologies. Clinical trial information: NCT03635892.

*Includes 16 unclassified with papillary features, 11 high grade papillary and 5 FH-deficient RCC.