This study follows earlier phase I and II trials showing remarkable responses in patients with advanced medullary thyroid carcinoma, some of whom had progressed on prior tyrosine kinase inhibitor therapy, explained formal discussant of this trial, Samuel A. Wells, MD, of the Center for Cancer Research at the National Cancer Institute, National Institutes of Health, Bethesda, Maryland.

Dr. Wells questioned the degree of censoring in this trial, because the numbers of patients censored did not appear to be consistent with the percentages for treatment response. He commented that he would have liked to know how many patients required dose reductions. In addition, he noted that overall survival might be confounded by patients who develop progressive disease on cabozantinib and subsequently receive another molecular targeted therapeutic once they are off the clinical trial.

Approximately 45% of patients with medullary thyroid carcinoma have either somatic RET or RAS mutations, but not both together. I would like to know if the authors detected RAS mutations, and if so, did the presence of either RAS or RET mutations correlate with clinical response? ■

Disclosure: Dr. Wells reported no potential conflicts of interest.