The Food and Drug Administration on Thursday confirmed three cases and a possible fourth of progressive multifocal leukoencephalopathy, or PML, which causes swelling of the brain and is usually fatal. All the cases were reported in the last six months.

The FDA announcement came the same day that European Union regulators recommended a ban on marketing the drug. The European Medicines Agency stated "the benefits of Raptiva no longer outweigh its risks, because of safety concerns."

The drug is marketed in Europe by Swiss drugmaker Merck Serono.

The FDA said two U.S. patients who were diagnosed with the disease died, as did the additional patient who was believed to have the disease, but was never diagnosed.

Genentech previously notified physicians and investors of the cases.

"We take the risk of PML very seriously and are working diligently with the FDA to put the right plans in place that will help protect patient safety," said company spokeswoman Tara Cooper.

First approved in 2003, Raptiva is a once-a-week injection used to treat red, scaly skin caused by psoriasis.

The FDA in October added its most serious warning to Raptiva, after a 70-year-old patient caught PML and died after taking the drug for four years.

The agency stressed in a statement posted to its Web site Thursday that patients should be aware of the symptoms of the infection, which include weakness, blurred vision and difficulty speaking. Doctors should likewise monitor patients taking the drug for these signs, the FDA said.

PML is typically seen in patients with weakened immune systems, and previously has been reported in patients taking Rituxan, a blockbuster arthritis and cancer drug marketed by Genentech and Biogen Idec.

Shares of Genentech added 6 cents to close at $84.76.