Business / Technology

WASHINGTON — Shares of biotech drugmaker Dendreon surged 16.7 percent Monday after federal health regulators published a critical review of rival Amgen's drug for prostate cancer.

Dendreon's lead product is the prostate cancer drug Provenge, which is designed to train a patient's immune system to fight the disease. It is approved only for patients with late-stage cancer who haven't responded to previous therapies.

Thousand Oaks, Calif.-based Amgen has asked the Food and Drug Administration to approve its injectable drug Xgeva as a preventive measure for men with recurring prostate cancer that is at high risk of spreading to the bones.

In documents posted online, FDA reviewers questioned the drug's benefit for patients, noting that it did not extend life and carried serious side effects. The drug did slow the spread of cancer to the bone by about four months.

Xgeva is already approved for preventing fractures in cancerous bones.

On Wednesday the FDA will ask a panel of outside experts whether the benefits of Amgen's Xgeva outweigh its risks, which included bone disease in about 5 percent of patients taking the drug. The FDA, which is not required to follow the group's advice, is scheduled to make its final decision on the drug by late April.

Shares of Seattle-based Dendreon rose $2.36 to $16.53 Monday. Amgen shares fell 16 cents, or 0.2 percent, to $69.12.

Provenge is Dendreon's only approved product. Since its FDA approval in April 2010 sales have been disappointing, in part because of the drug's high price and concerns that it does not extend patient's lives by a great deal. Dendreon sharply cut its expectations for sales of Provenge in 2011.