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ASCO '13: Onyx's Nexavar Delays Growth of Thyroid Cancer

CHICAGO (TheStreet) -- Onyx Pharmaceuticals' (ONXX) Nexavar stalled disease progression by five months in patients with treatment-resistant, differentiated thyroid cancer, an aggressive form of the disease that has gone without new, effective therapies for 40 years.

Based on the positive Nexavar phase III results, Onyx and its partner Bayer will file for FDA approval in the middle of the year. Nexavar is already approved for the treatment of kidney cancer and liver cancer, with 2012 sales of $861 million.

Differentiated thyroid cancer is the most common subtype of thyroid cancer and has generally high cure rates when treated with surgery or radioactive iodine. Five to 15 percent of differentiated thyroid patients can develop resistance to radioactive iodine. When that happens, these patients have no effective treatment options.

Onyx believes Nexavar, if approved, could become a new treatment option for 3,000 to 4,000 patients annually in the U.S. diagnosed with radioactive iodine-refractory, differentiated thyroid cancer. An equal number of these patients are diagnosed in Europe.

"Thyroid cancer is another growth driver for Nexavar internationally and domestically," said Onyx CEO Tony Coles. "Thyroid cancer patients can live two to two-and-a-half years once their disease becomes refractory, so the opportunity for us with Nexavar is longer dosing over that time..." compared to Nexavar's use in liver and kidney cancer.

Nexavar does have a U.S. compendia listing in thyroid cancer already which allows for insurance reimbursement. Coles believes there is already "some" use of Nexavar in U.S. thyroid cancer patients but the company does not have specific numbers.

In the phase III studies, 417 patients with differentiated thyroid cancer that no longer responds to radioactive iodine were randomized to treatment with Nexavar or placebo. Following treatment, Nexavar delayed the time to regrowth of tumors (progression-free survival) by a median of 10.8 months compared to a median of 5.8 months with the placebo.

Overall, Nexavar reduced the risk of disease progression by 42 percent compared to placebo -- a statistically significant benefit which met the primary endpoint of the study.

Clinically meaningful tumor shrinkage was seen in 30 percent of Nexavar-treated patients compared to 0.5 percent of placebo patients.

The study allowed placebo patients to cross over and receive Nexvar once their tumors started to grow again. Seventy-one percent of placebo patients received Nexavar as well, which adversely impacted the overall survival analysis in the study. Nexavar reduced the risk of death by 20% compared to placebo, but the survival benefit was not statistically significant.

The common side effects attributed to Nexavar treatment were hand-foot skin reaction, diarrhea, hair loss, rash and fatigue. Nineteen percent of patients treated with Nexavar discontinued from the study due to side effects compared to 4% of patients treated with placebo.

"After having no effective drugs for these patients for so many years, it is very exciting to find an oral drug that stops growth of the cancer for several months," said Dr. Marcia Brose of the Abramson Cancer Center at the University of Pennsyslvania.

Full results from the Nexavar thyroid cancer study are being presented Sunday afternoon during the plenary session of the American Society of Clinical Oncology (ASCO) annual meeting.

-- Reported by Adam Feuerstein in Chicago.

Adam Feuerstein writes regularly for TheStreet. In keeping with company editorial policy, he doesn't own or short individual stocks, although he owns stock in TheStreet. He also doesn't invest in hedge funds or other private investment partnerships. Feuerstein appreciates your feedback; click here to send him an email.

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