In this study, researchers estimated that cabozantinib have shown efficacy in the first-line treatment of radioactive iodine (RAI)–refractory differentiated thyroid carcinoma (DTC) and could offer an option in addition to the drugs approved for this indication, such as sorafenib and lenvatinib.

New data from a phase 2 study showed that patients with thyroid cancer that progressed after surgery and RAI achieved an objective response rate of 54% with cabozantinib, and tumor shrinkage was seen in 34 of the 35 enrolled patients. Patients whose disease is refractory to RAI have the option to be treated with sorafenib or lenvatinib, both vascular endothelial growth factor receptor (VEGFR) inhibitors.

She noted, however, that responses to these drugs are not durable and patients need additional therapies. Cabozantinib is a multikinase tyrosine kinase inhibitors targeting VEGFRRETMET, and AXL and is already approved for use in patients with advanced thyroid cancer and renal cell carcinoma.

The manufacturer is exploring other indications. "Based on these promising results and data from other studies of cabozantinib in previously treated DTC, Exelixis plans to initiate a pivotal phase 3 study with cabozantinib in patients with advanced DTC later this year," Gisela Schwab, MD, company president and chief medical officer, said in a statement.

Brose presented data from the UPCC 28313 (NCT 02041260)  study, which enrolled 35 patients with metastatic, RAI-refractory thyroid cancer who had not received prior treatment with VEGFR inhibitors. Median age at enrollment was 65 years, and three fourths of the patients had papillary thyroid cancer.

The study was powered to detect an overall response rate of 15%, which translates to responses in at least 5 of the 35 patients. Although no patient showed a complete response, partial responses were seen in 19 of 35 (54%) patients and stable disease was reported for 15 of 35 (43%) patients. Duration of partial response ranged from 11 weeks to more than 174 weeks.

Stable disease lasting for greater than 6 months was seen in 9 of 35 (26%) patients and ranged from 8 weeks to more than 142 weeks. Most common adverse events were hyperglycemia (80%), diarrhea (77%), malaise/fatigue (74%), and weight loss (71%). Grade 3/4 adverse events occurring in more than one patient were hypertension (14%), increased lipase (9%), pulmonary embolism (6%), and hyponatremia (6%).

However, she said that cabozantinib will need to be further evaluated in phase 3 studies and that the design of such a study is underway. When questioned about whether the drug is available to patients, When the drug becomes available, Brose said that three good drugs will be available to patients in the first-line setting. For patients with indolent disease, sorafenib and lenvatinib are both viable options.

Over 90% of patients have good performance status even after two therapies, and a third one will fill a high unmet need.