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WEDNESDAY, July 2 (HealthDay News) -- An experimental drug that inhibits tumor blood vessel formation slows the progression of metastatic thyroid cancer in some patients, an international study finds.

Of the 93 patients with rapidly progressing cancer, 49 had a positive response to treatment with motesanib diphosphate. Of those 49 patients, 14 percent had their tumors shrink and 35 had their tumors stabilize for more than 24 weeks. Median progression-free survival was about 40 weeks.

Genetic analysis of 25 patients revealed that drug response was better in those with a mutation known as BRAF V600E in their tumors than in those without the mutation. Further research into this genetic connection is needed, the researchers said.

"Finding that patients whose tumors bear a particular mutation were more likely to respond to the drug is an example of where we would like to head in our research," study author Dr. Steven I. Sherman, chairman and professor of the department of endocrine neoplasia and hormonal disorders at the University of Texas M.D. Anderson Cancer Center, said in a prepared statement.

"This is the first of the various thyroid cancer trials to identify specific mutations that might allow us to individualize or personalize therapy," he said.

The study, published in the July 3 issue of the New England Journal of Medicine, was funded by drug maker Amgen Inc.

Motesanib diphosphate -- a VEGF inhibitor -- targets a protein called vascular endothelial growth factor (VEGF), which plays a critical role in the formation of new blood vessels that allow tumors to grow and spread.

Currently, there are few treatment options for metastatic thyroid cancer.

"There is no standard accepted chemotherapy for advanced metastatic differentiated thyroid cancer, and response rates have typically been 25 percent or less," Sherman said. "Most patients are not treated with systemic chemotherapy, because the limited benefit rarely justifies the side effects. Treatment of thyroid cancer has been a completely unmet need."

More information

The American Cancer Society has more about thyroid cancer.