Amgen Inc. and Johnson & Johnson's anemia drugs may raise the risk that patients with a bone marrow disease will later develop leukemia, according to an analysis of 30 years of patient records, Bloomberg News reports.

Mayo Clinic researchers reviewed records of 311 patients with primary myelofibrosis, a scarring of the bone marrow, from 1976 to 2006. Amgen's Aranesp and Epogen and Johnson & Johnson's Procrit were linked to leukemia among 27 patients that developed the disease, according to research presented today at the American Society of Hematology meeting today in Atlanta.

Past studies linked anemia drugs to heart attack, stroke and death when used in high doses. Warnings from U.S. regulators about the risks caused U.S. sales of Aranesp to drop 36 percent in the third quarter. Aranesp is Amgen's biggest product, with $4.12 billion in sales in 2006.

``We believe this to be the first large, systematic evaluation of the risk factors leading to leukemic transformation in primary myelofibrosis,'' said Jocelin Huang, a hematology researcher at Mayo Clinic, in a statement. ``In the process, we discovered some unexpected results.''

Amgen fell $1.11, or 2.1 percent, to $50.99 at 4 p.m. New York time in Nasdaq Stock Market composite trading. The stock has lost 25 percent this year. Earlier today, Sanford C. Bernstein & Co. analyst Geoffrey Porges downgraded Amgen to ``market perform'' from ``outperform.'' J & J; added 11 cents to $67.79 in New York Stock Exchange composite trading.

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