LAKE BUENA VISTA, FLA. – Most patients with differentiated thyroid cancer who had shown progression on previous courses of targeted chemotherapy either maintained stable disease or responded to the oral multikinase inhibitor cabozantinib (Cometriq), according to a small multicenter phase II trial presented at the International Thyroid Congress.
This is important, according to Dr. Manisha H. Shah, because there has been no standard of care for patients with differentiated thyroid cancer whose cancer progresses on first- or second-line vascular endothelial growth factor receptor (VEGFR) inhibitors.
Nine of the 25 enrolled patients (36%; 95% confidence interval, 18%-57%) showed confirmed partial response, 12 patients (48%) had stable disease, and one patient had disease progression, according to Dr. Shah, director of the neuroendocrine tumor program at Ohio State University’s Wexner Medical Center. The trial enrolled patients with radioiodine–refractory differentiated thyroid cancer who had progression of their disease after one or two previous VEGFR agents.
Cabozantinib targets VEGFR and MET and is approved as first-line treatment for medullary thyroid cancer. The majority of the response to cabozantinib occurs in the first several months of treatment, so the study used a Simon minimax two-stage design, enrolling an initial 16 patients, then opening enrollment to an additional 9 when at least 2 of the initial cohort showed partial or complete response within the first 6 months.
The primary outcome measure was the number of patients showing objective response (partial or complete response) within the first 6 months of therapy.
Median patient age was 64 years, and 64% of patients were male. Just over half of the patients previously had been treated with sorafenib, and just over a quarter had received pazopanib. Five patients had received two previous VEGFR-targeted therapies, while the remaining 20 had received one.
Nine patients (36%) had papillary thyroid cancer, seven (28%) had poorly differentiated thyroid cancer, five (20%) had Hurthle cell cancer, and four (16%) had follicular thyroid cancer. The most common metastasis sites were lymph node, bone, and lung.
Patients received continuous treatment until they showed disease progression, had an unacceptable adverse event or an illness precluding further treatment, or withdrew consent.
Disease progression was measured by serum tumor markers and CT or MRI scan every 8 weeks while in the study; patients also received bone scans and 18F-FDG and 18F-fluoride PET scans before the study and while in the study.
Side effects were common and generally mild, with two instances each of grade 3 events related to fatigue, hand-foot skin reactions, and diarrhea. One death occurred and was adjudicated as possibly study related; there were no grade 4 events, and no grade 3 bleeding events.
Dr. Shah noted that the starting cabozantinib dose of 60 mg/day was considerably lower than that used in previous trials for thyroid cancer. With time, investigators have learned that the sometimes debilitating side effects of cabozantinib are somewhat dose dependent, she noted. The study design permitted dose escalation to 80 mg for nonresponders to the lower dose, and permitted a decrease to 40 or 20 mg/day as needed to manage side effects. Investigators were able to tell the patients what to expect, and to be proactive in anticipating side effects. “We have learned to manage these drugs much better with time,” she said.
“Cabozantinib was effective in inducing a durable partial response,” said Dr. Shah. Future directions, in addition to phase III clinical trials, may include combining cabozantinib with immune checkpoint–targeted therapies such as lenvatinib, a strategy that has been effective for other cancers, she said at the meeting, which was held by the American Thyroid Association, Asia-Oceania Thyroid Association, European Thyroid Association, and Latin American Thyroid Society.
The multisite study was sponsored by the National Cancer Institute with participation by eight International Thyroid Oncology Group centers. Dr. Shah reported being on the advisory board for Exelixis and Eisai, and receiving research funding from those two organizations and Bayer.
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