Regulators are requesting more information from Celgene ( CELG) to support the biotech company's bid to get its leprosy treatment Thalomid approved for fighting blood cancer.

The Food and Drug Administration conditionally approved Celgene's application but said it wants to see updated safety information, additional patient data and revised product labeling before it makes a final decision.

Though Thalomid is FDA-approved specifically for treating leprosy, the majority of prescriptions for the drug are written for multiple myeloma, a progressive blood disease. The condition is a cancer of the plasma cell, a key part of the immune system that makes antibodies to help fight infection and disease.

Since the agency has already approved the drug for one indication, doctors are allowed by law to prescribe it for other purposes as they see fit, through what's known as "off-label" use.

Celgene's application to market Thalomid for multiple myeloma was based on the results of a late-stage trial comparing the drug in combination with the steroid dexamethasone to dexamethasone alone in previously untreated multiple myeloma patients.

"Based on ongoing discussions with the FDA we expect to complete our responses to these requests quickly," said Dr. Graham Burton, senior vice president of Celgene's regulatory affairs.

Thalomid, more commonly known as thalidomide, can cause severe birth defects if it's taken during pregnancy, and it's capable of leading to potentially severe, permanent nerve damage. The drug was approved for treating leprosy in 1998.

Originally, thalidomide was marketed as a sedative outside the U.S., and some women took it to alleviate morning sickness before it was linked with birth defects.

Celgene shares were unchanged at $59.90 Tuesday.

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