Heightened safety concerns over Amgen Inc.'s popular anemia drugs Aranesp and Epogen, as well as Johnson & Johnson's Procrit has prompted a review by federal health insurance officials.

The Centers for Medicare and Medicaid Services will study "off-label" uses of the drugs, such as treatment of anemia in cancer patients not undergoing chemotherapy, to determine whether the Medicare program will continue paying for them.

Combined sales of Aranesp and Epogen totaled more than $6 billion worldwide for Amgen in 2006.

Shares of Thousand Oaks-based biotech giant Amgen Inc. have lost 20 percent since a study was released by Danish researchers in January indicating the "off-label" uses of the anemia drugs in cancer patients could actually increase the risk of additional cancer.

Shares of Amgen were down 53 cents to $60.16 in afternoon trading Thursday on the Nasdaq.

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