SOUTH SAN FRANCISCO, Calif. ( TheStreet) -- Oxigene ( OXGN) reported Sunday that the overall survival of patients with advanced thyroid cancer was boosted after treatment with the company's experimental cancer drug zybrestat. However, zybrestat results from the late-stage study were negatively impacted by a sharp reduction in the number of patients enrolled and were therefore not statistically significant.

Oxigene also made no mention in its Sunday announcement about seeking regulatory approval for zybrestat based on the new thyroid cancer data, but the company is conducting other studies of the drug, including a phase II in patients with non-small cell lung cancer.

Investors whistled past them mixed results Monday, pushing Oxigene shares up 48% to 40 cents a share in the pre-market trading session.

At a European thyroid research meeting Sunday, researchers said that patients with anaplastic thyroid cancer (ATC) who were treated with a combination of zybrestat and chemotherapy demonstrated a median overall survival of 5.1 months compared to a median overall survival of 4.1 months for similar patients treated with chemotherapy alone.

The results translated into a 29% reduction in the risk of death for zybrestat-treated patients, said Oxigene.

However, the phase II/III study enrolled just 80 patients (55 in the zybrestat arm, 25 in the control arm), down from a planned enrollment of 180 patients. Enrollment was cut short because investigators could not find enough patients to enroll in the study. As a result, a statistical analysis of the survival benefit was not performed.

Researchers presenting the zybrestat data Sunday at the thyroid meeting in Paris also acknowledged that the one-month survival benefit observed would not have been statistically significant even if the study had been fully enrolled.

Nonetheless, Oxigene CEO Peter Langecker called the new zybrestat data a "major improvement over current standard of care for ATC patients" and said the data have "positive implications for future development in other cancer indications."

Zybrestat belongs to a class of cancer drugs known as vascular disrupting agents (VDAs) that are designed to target and destroy blood vessels within tumors, thereby depriving them of oxygen and nutrients. VDAs are supposed to work against existing or more mature tumor blood vessels, compared to anti-angiogenesis inhibitors like Roche's Avastin, which work by preventing tumors from developing new blood vessels.

So far, Oxigene has yet to demonstrate conclusively the efficacy of zybrestat although Sunday's data are another potentially positive signal. Earlier this year, Oxigene presented interim results from a phase II study in non-small cell lung cancer patients that showed some early indication that patients benefited from the addition of zybrestat to a standard treatment consisting of Avastin plus chemotherapy.

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