Extended Disease Control with Unconventional Cabozantinib Dose Increase in Metastatic Renal Cell Carcinoma

BACKGROUND: Cabozantinib is among the most potent tyrosine kinase inhibitors (TKIs) FDA-approved for metastatic renal cell carcinoma (mRCC). Effective treatments after progression on cabozantinib salvage therapy are limited. Dose escalation for other TKIs has been shown to afford added disease control. OBJECTIVE: We sought to evaluate whether dose escalation of cabozantinib (Cabometyx®) from conventional doses in select patients with limited treatment options offered additional disease control. We asked how cabozantinib dose increases may affect circulating drug levels. METHODS: We identified patients with mRCC at the University of Texas Southwestern Medical Center who were treated with cabozantinib dose escalation to 80 mg after progressing on conventional cabozantinib 60 mg. We then queried leading kidney cancer investigators across the world to identify additional patients. Finally, we reviewed pharmacokinetic (PK) data to assess how higher doses impacted circulating levels by comparison to other formulations (Cometriq® capsules). RESULTS: We report six patients treated at two different institutions with cabozantinib-responsive disease and good tolerability, where cabozantinib was dose escalated (typically to 80 mg, but as high as 120 mg) after progression on 60 mg, a strategy that resulted in added disease control (median duration, 14 months; 95% Confidence Interval [CI]: 8 -Not Estimable[NE]). Four patients (66.7%) had disease control lasting at least 1 year. No grade III/IV adverse events were identified in this small, select, cohort. A comparison of PK data to FDA-approved cabozantinib 140 mg capsules suggests that cabozantinib 80 mg tablets results in comparable exposures. CONCLUSIONS: mRCC patients with cabozantinib responsive disease and reasonable tolerability may benefit from dose escalation at progression.