Exelixis shares plunge on prostate cancer drug study protocols

Exelixis Inc., a biotechnology company with no approved products, fell 31 percent in early trading after failing to agree with U.S. regulators on special rules for a study of its experimental prostate cancer drug.

Instead, Exelixis will begin the late-stage clinical trial of the treatment, cabozantinib, by the end of 2011 under the “normal regulatory framework,” after the company and the Food and Drug Administration couldn’t reach agreement on how the study should be conducted and its results measured, Michael Morrissey, chief executive officer of the South San Francisco, California-based company, said yesterday in a statement.

Exelixis dropped $2.43 to $5.30 at 7:24 a.m. New York time. The company’s shares have declined 5.9 percent his year.

The company also is studying cabozantinib in thyroid cancer and has said it would apply for marketing approval of the drug for that use in the first quarter of 2012. Frank Karbe, Exelixis chief financial officer, said Oct. 27 during a conference call that the company “remained confident” it would reach an agreement with the FDA on the prostate cancer clinical trial.