Exelixis, Inc. and Ipsen announced detailed results from the phase 3 COSMIC-311 pivotal trial of cabozantinib (CABOMETYX®) in patients with previously treated radioactive iodine-refractory differentiated thyroid cancer (DTC). Results from the trial, which met the co-primary endpoint of significant improvement in progression-free survival (PFS) assessed by blinded independent radiology committee (BIRC), are in press to be published in The Lancet Oncology and have been submitted to the U.S. Food and Drug Administration (FDA). Results from COSMIC-311 served as the basis for the supplemental New Drug Application that Exelixis has submitted to the FDA, seeking an expanded indication for CABOMETYX for patients 12 and older with DTC that has progressed following prior therapy and who are radioactive iodine-refractory (if radioactive iodine is appropriate).

As previously announced, at a planned interim analysis, cabozantinib demonstrated a significant reduction in the risk of disease progression or death of 78% versus placebo (hazard ratio [HR]: 0.22; 96% confidence interval [CI]: 0.13-0.36; P0.0001) in the intent-to-treat (ITT) population. At a median follow-up of 6.2 months, median PFS was not reached (96% CI: 5.7 months – not estimable) in patients treated with cabozantinib and was 1.9 months (96% CI: 1.8-3.6 months) for placebo. The data presented at the 2021 ASCO Annual Meeting demonstrate that HRs for PFS consistently favored cabozantinib over placebo for prespecified subgroups, including age 65 vs.

>65; prior treatment with lenvatinib (yes vs. no), and number of prior vascular endothelial growth factor receptor (VEGFR)-targeting therapies (1 vs. 2).

The results for the co-primary endpoint of objective response rate in the first 100 randomized patients after six months favored cabozantinib at 15% versus 0% for placebo, although this difference was not statistically significant (P=0.028). In the ITT population, a reduction in target lesion size was found in 76% of patients receiving cabozantinib versus 29% of patients receiving placebo; median overall survival was not reached in either treatment arm but favored cabozantinib (HR: 0.54; 95% CI: 0.27-1.11).