The trial tested pomalidomide plus a low dose of dexamethasone, a standard treatment, and compared it with a high dose of dexamethasone alone.

Data showed patients who had failed an average of five previous therapies who took pomalidomide and low-dose dexamethasone survived significantly longer than those who took high-dose dexamethasone.

The company had previously reported that the drug improved survival, but the new data, the result of an interim analysis, show that no matter what occurs during the remainder of the trial, the improvement in overall survival will be highly significant.

The median overall survival for patients in the pomalidomide arm of the trial has not yet been reached, while the median overall survival in the control arm was 34 weeks.

From a statistical perspective, the results reflect "a very meaningful reduction in the risk of death for these refractory patients," said Brian Abrahams, an analyst at Wells Fargo Securities.

Detailed results will be presented in December at the annual meeting of the American Society of Hematology.

The company had previously reported that the drug also improved progression-free survival, or the length of time patients lived before relapsing, but did not give the magnitude of improvement.

The new data shows pomalidomide nearly doubled that time to 15.7 weeks from 8 weeks in the control arm.

Celgene hopes the data will add weight to its application for marketing approval of the drug. The company has already filed an application with U.S. and European health regulators based on data from a mid-stage trial that tested pomalidomide plus low-dose dexamethasone against pomalidomide alone.

Median progression-free survival in that trial, the main goal of the study, was 4.7 months in the pomalidomide plus low-dose dexamethasone arm compared with 2.7 months in the pomalidomide alone arm.

Multiple myeloma is a cancer that starts in plasma cells in bone marrow and ultimately disrupts the production of normal blood cells.

Geoff Meacham, an analyst at J.P. Morgan, estimates pomalidomide could generate sales of around $450 million by 2015. In July, Celgene's chief executive, Robert Hugin, said he expects pomalidomide to eventually generate annual sales of more than $1 billion.

A decision from the U.S. Food and Drug Administration on whether to approve the drug is expected by February 10.

Celgene already sells the multiple myeloma drug Revlimid for patients at earlier stages of disease. Patients in the pomalidomide trial had failed to respond to Revlimid.

Celgene's shares rose 0.8 percent to $74.94 in afternoon trading on Nasdaq. Earlier they rose as high as $76.10.

(Reporting By Toni Clarke)

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