SOUTH SAN FRANCISCO (TheStreet) -- Sunesis Pharmaceuticals (SNSS) announced the failure of a phase III study Monday morning. The company's experimental drug vosaroxin did not extend survival of elderly patients with advanced acute myeloid leukemia compared to a placebo.

In the phase III study of 711 elderly AML patients, treatment with vosaroxin reduced the risk of death by only 13% compared to a placebo. The survival trend was not statistically significant, failing the primary endpoint of the study. At the median, vosaroxin patients lived 7.5 months compared to 6.1 months for placebo patients.

Sunesis performed another analysis of the study excluding AML patients who later underwent a stem cell transplant. In this subgroup analysis, vosaroxin reduced the risk of death by 19% compared to placebo, which was statistically significant. At the median, the survival benefit was 6.7 months for vosaroxin patients compared to 5.3 months for placebo patients.

There was no explanation offered by Sunesis for why vosaroxin patients undergoing subsequent stem cell transplant would have shorter median survival.

Based on the failed study, Sunesis said it would seek approval of vosaroxin in Europe. No explanation was offered for why European regulators would approve the drug based on a failed phase III study.

Sunesis shares closed Friday at $6.64. Monday morning before the bell, shares were trading down over 70% to $1.94.

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.