The investigational drug axitinib produced tumor regression or stable disease in almost three-out-of-four patients with advanced thyroid cancer, a research team reported at the annual meeting of the American Society for Clinical Oncology in Chicago.
In this exploratory phase-2 trial, 18 out of 60 patients (30%) had their tumors shrink by 31 to 83 percent. Another 25 patients (42%) had stable disease, with no tumor progression or slight reduction in size, when measured at four months. Many of those patients still have stable disease.
"This is exciting," said study presenter Ezra Cohen, MD, PhD, assistant professor of medicine at the University of Chicago. "Until now we really didn't have anything to offer thyroid cancer patients with advanced disease that was refractory to standard measures."
Although this drug did not produce complete responses, it appears to have caused "significant tumor reduction in most subjects," he added, "Axitinib has prevented the disease from progressing in most patients, and in a lasting way."
In this trial, which began nearly three years ago, "the median duration of stable disease has not been reached," Cohen said. "Twenty-four patients are still in treatment."
Axitinib is a small molecule designed to prevent tumors from acquiring the blood supply they need to grow. It blocks all three known receptors for a substance called vascular endothelial growth factor (VEGF), a biologic factor tumors release in order to grow new blood vessels in the tumor, a process called angiogenesis.
The study confirmed that the drug worked as predicted. Treatment significantly reduced the presence of soluble VEGF receptors, VEGFR2 and VEGFR3, in blood. Levels of VEGF in the blood increased, suggesting that this growth factor was compensating for angiogenesis inhibition by axitinib.
More importantly, it prevented tumor growth. In only 10 out of 60 patients (17%) did the tumors continue to grow. Another 18 patients left the trial for other reasons, including toxicity. Five of them withdrew because of treatment-related adverse events.