Efficacy of cabozantinib (XL184) in patients (pts) with metastatic, refractory renal cell carcinoma (RCC).

Abstract

4504 Background: Cabozantinib (cabo) is an oral, potent inhibitor of MET and VEGFR2 that is currently undergoing evaluation in several oncology indications. Renal cell carcinoma (RCC) was chosen as an indication in this drug-drug interaction (DDI) study based on involvement of the MET and VEGFR signaling pathways in this disease. The primary objective of this study is to determine the effect of cabo on single dose PK of the CYP2C8 substrate rosiglitazone (rosi). Anti-tumor activity was also evaluated. Methods: Eligible pts were required to have RCC with clear cell components with metastases, Karnofsky performance status of ≥70 and measurable disease by RECIST. Pts needed to have experienced PD following standard therapies. Cabo was given daily at a dose of 140 mg free base (equivalent to 175 mg salt form) starting at Day 2. Rosi (4 mg) was given Day 1 and Day 22 to complete PK assessment for DDI. Cabo was continued until PD. On Day 57 and every 8 weeks thereafter subjects underwent tumor assessments by mRECIST. Results: Enrollment is complete at 25 RCC pts; 17/25 (64%) RCC pts had received ≥ 2 prior agents; 13/25 (52%) with at least 1 VEGF pathway inhibitor and 1 mTOR inhibitor. The majority of pts were in an intermediate (21/25) or poor (3/25) prognostic category (1/25 in favorable category) per Heng et al (JCO, 2009, v27, p5794). ORR by mRECIST: 7/25 (28%). Disease control rate (PR + SD): 72% at 16 weeks; 19/21 (90%) pts with ≥1 post-baseline scan experienced tumor regression (range: 4 - 63% reduction in measurements). 10/25 (36%) pts remain on cabo. Median PFS is 14.7 months (95% CI: 7.3, upper limit not reached) with a median follow-up of 7.7 months. AEs ≥ Grade 3 severity: hypophosphatemia (36%), hyponatremia (20%), and fatigue (16%). PK data suggest that clinically relevant doses of cabo do not alter the Cmax or AUC0-24h of rosi, consistent with no inhibition of CYP2C8. Conclusions: Cabo demonstrates encouraging anti-tumor activity in heavily pretreated RCC pts with a toxicity profile similar to that of other VEGFR TKIs. PK data suggest no DDI between cabo and rosi (CYP2C8 substrate).