CORRECTED - UPDATE 1-Cancer drug slows multiple sclerosis progression

(Corrects shots to infusions in first paragraph) (Adds details and quotes)

By Gene Emery

BOSTON, Feb 13 (Reuters) - Two infusions of the cancer drug Rituxan given two weeks apart slowed the progression of multiple sclerosis for nearly a year, researchers reported on Wednesday.

And Rituxan appears to be twice as effective as first-line treatments for MS, which reduce the number of relapses by about a third, the researchers said.

"It's quite remarkable that the effect was sustained for 48 weeks with just a single course of therapy," said Dr. Stephen Hauser of the University of California at San Francisco, who worked on the study published in the New England Journal of Medicine.

Multiple sclerosis, which affects as many as 350,000 people in the United States and 2 million worldwide, is apparently caused when the immune system attacks and breaks down the insulation surrounding cells that make up the brain and spinal cord.

MS symptoms may include blurred vision, loss of balance, poor coordination, extreme fatigue, paralysis and blindness. There is no cure.

Although no head-to-head comparison has been done, Hauser said Rituxan appears to work better than existing therapies.

His team tested patients with the relapsing-remitting form of the disease, in which symptoms wax and wane over many years, making it difficult to gauge whether a treatment is really working. They make up about half the patients with MS.