Background: Cabo shows robust clinical activity in mRCC. Patients (pts) with BM have been underrepresented in clinical trials and effective systemic therapy is lacking. We retrospectively characterized the clinical activity and toxicity of cabo in pts with BM from RCC. Methods: Consecutive medical records from mRCC pts with BM treated with cabo monotherapy across 15 institutions were reviewed. Pts were grouped by radiologic presence (cohort 1) or absence (cohort 2) of progressing intracranial metastases. Brain-directed local therapy was allowed but radiological confirmation of intracranial progression at cabo start was required in cohort 1. Radiological response rate was investigator-assessed by modified RECIST 1.1 for intracranial and RECIST 1.1 for extracranial responses. Time to treatment failure (TTF) and overall survival (OS) were estimated by Kaplan-Meier. Results: We identified 69 pts with BM from RCC, 25 (36%) in cohort 1 and 44 (64%) in cohort 2. Majority were IMDC intermediate/poor (87%) and received cabo as ≥2nd line (75%). Median time from mRCC diagnosis to BM was 19.1 months (mos) (IQR 4.4-39.5). Overall, median number of BM was 3 (range 1-27) and median size of largest lesion was 1.2 cm (range 0.2-6.6) with frontal (62%) and parietal (48%) as the most frequent localizations. Prior brain directed therapy was used in 65% and 93% of pts in cohort 1 and 2 respectively. Median follow-up after cabo initiation was 11 mos (range 4-72). Twenty three percent of pts remained on therapy while 52% discontinued for progression and 9% for toxicity. Intracranial response rate was 61% (95%CI 39%-80%), with 3 complete responses, for cohort 1 and 57% (95%CI 41%-72%) for cohort 2. Only 10% (n = 7) had intracranial progression as best response. For cohort 1, extracranial response was 52% (95%CI 31%-72%), median TTF was 9.9 mos (95%CI 5.9-14.0) and OS was 14.7 mos (95%CI 7.7-23.0). For cohort 2, extracranial response was 41% (95%CI 26%-57%), TTF was 9.0 mos (95%CI 4.6-11.4) and OS was 14.1 mos (95%CI 11.0-22.0). Most common adverse events were fatigue (77%) and diarrhea (46%). Eight pts received concomitant brain-directed treatment during cabo therapy without neurological toxicities. Conclusions: Cabo shows significant intracranial activity and acceptable safety profile in pts with BM from RCC.

* 4 pts excluded as BM < 5 mm