UPDATE 2-U.S. FDA to ask panel about anemia drug limits

(Adds FDA staff, company, analyst comments, updated shares)

By Lisa Richwine

WASHINGTON, March 11 (Reuters) - U.S. health officials will ask an advisory panel whether they should withdraw the approval of Amgen Inc (AMGN.O: Quote, Profile, Research) and Johnson & Johnson (JNJ.N: Quote, Profile, Research) anemia drugs for cancer chemotherapy patients or take other steps to minimize risks, documents released on Tuesday said.

Food and Drug Administration staff pointed to eight studies that showed evidence of harmful effects, including shorter survival or faster tumor growth, when used at high doses.

"There is now mounting evidence of documented effects on survival, tumor progression, and thrombotic (clotting) events which require a reassessment of the net benefits of this class of drugs," FDA staff wrote in an analysis prepared for a panel of outside experts that meets Thursday.

The panel is set to review the risks of the drugs -- which include Amgen's best-selling drug, Aranesp, and Johnson & Johnson's Procrit -- when given to cancer patients. The drugs also are sold for patients with kidney disease.

Amgen shares fell 1.3 percent to $44.12 in afternoon trading on Nasdaq. Shares of Johnson & Johnson gained 1 percent to $61.93 on the New York Stock Exchange.

Aranesp sales were $3.6 billion in 2007, while Procrit sales hit $2.9 billion. Procrit is much less important to diversified health-care company Johnson & Johnson than Aranesp is to the smaller Amgen.

The drugs, known as erythropoiesis-stimulating agents (ESAs), are genetically engineered versions of a protein that boosts production of oxygen-carrying red blood cells.