Mayo investigators reported that cancer in about two-thirds of 37 patients with aggressive differentiated thyroid cancer treated with the drug Pazopanib ( Votrient ) either stopped growing, or quickly shrank.

The patient responses are promising, the researchers say, because all patients had fast-growing cancers that had spread to their lungs, with half involving lymph nodes and 39 percent also involving bones.

Approximately one-third of patients achieved sustained and dramatic benefit from Pazopanib, while another one-third experienced stabilization of their cancer or some tumor shrinkage. The remaining one-third of patients did not benefit from the drug. The agent was also well tolerated by the majority of patients.

What is not yet known, however, is the drug's effect on overall survival.
Of the 37 original trial participants, two have died - one from cancer progression and another from other causes.

The National Cancer Institute ( NCI ) estimated that 37,340 new cases of thyroid cancer would be diagnosed in 2008, with 1,590 deaths from the cancer. The cancer is much more common in women; it is the seventh most common cancer in women in the U.S. The occurrence of thyroid cancer has recently been rising.

Most thyroid cancers are of two major differentiated types - papillary thyroid cancer ( the most common, accounting for 75 percent of cases ) and follicular thyroid cancer ( 15 percent ).

Most patients with thyroid cancer respond well to surgery and to follow-up treatment with radioiodine; even if the cancer recurs and spreads, the disease progresses slowly in most patients. However, about 5 percent of the patients experience rapidly progressing life-threatening disease that is insensitive to radioiodine and other treatment approaches.

Pazopanib is an antitumoral agent that is also being studied in advanced kidney, ovarian and other cancers. The drug, administered in pill form, targets proteins involved in angiogenesis, the growth of new blood vessels that has a critical role in the growth and spread of tumors. The proteins that Pazopanib targets include vascular endothelial growth factor receptor ( VEGFR ), platelet-derived growth factor receptor ( PDGFR ), c-kit and Ret.

Source: Mayo Clinic, 2009

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