5547 Background: Cabozantinib (cabo) is an oral, potent inhibitor of MET, VEGFR2, and RET that is currently undergoing evaluation in several oncology indications. Differentiated thyroid cancer (DTC) pts were included in this study based on involvement of the MET, VEGFR, and RET 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 and safety were also evaluated. Methods: Metastatic DTC pts who were enrolled to this study were required to be RAI-refractory, have progressed on standard therapies and have measurable disease. Cabo was given daily at a dose of 140 mg free base (equivalent to 175mg salt form) starting at Day 2. Rosi (4mg) was given Day 1 and Day 22 to complete PK assessment for drug-drug interaction (DDI). Cabo was continued until PD. On Day 57 and every 8 weeks thereafter subjects underwent tumor assessments by mRECIST. Results: 15 DTC pts were enrolled. Median number of prior regimens was 2 (11/15 pts had at least 1 prior VEGFR inhibitor). 8/15 pts (53%) had confirmed PRs including 1 pt with marked improvement of a bone infiltrating lesion; 6 (40%) had best response of SD; all 14 pts with ≥1 post-baseline scan experienced tumor regression (range: -9 to -55%). Disease control rate (PR + SD): 80% at 16 weeks; 10/15 (67%) remain on cabo with a median follow-up of 7.3 months. Median PFS and OS have not been reached. Most common Gr 3/4 AEs were: diarrhea (20%), lipase increased (20%), hypertension (13%) and palmar-plantar erythrodyesthesia (13%); one related Gr 5 event reported: hemoptysis due to aorto-trachael fistula in a pt with history of prior mediastinal XRT and extensive neck surgeries. PK data suggest that clinically relevant doses of cabo do not alter the C max or AUC 0-24h of rosi, consistent with no inhibition of CYP2C8. Conclusions: In pts with DTC, cabo treatment resulted in substantial anti-tumor activity. The safety profile of cabo was comparable to that seen with other VEGFR TKIs. PK data suggest no DDI between cabo and rosi (CYP2C8 substrate).
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Cabanillas et al. (2012) studied this question.