Amgen’s stock stock fell $6.50 to $31.75 a share.

The stock drop was due to a report that Genetics Institute, a Cambridge, Mass., biotech firm, has been issued a U.S. patent on a form of erythropoietin (EPO), a protein that helps control the production of red blood cells. Both Genetics Institute and Amgen have been testing EPO in clinical trials. Analysts said, however, that Amgen appears to have the lead in the patent race for another form of EPO, which could eventually lead to a cross-licensing agreement between the two firms. About 3.4 million shares of the Thousand Oaks biotechnology firm’s shares were traded on NASDAQ, 30 times its normal volume.