Genentech Inc. and Biogen Idec Inc.‘s cancer drug Rituxan improved symptoms of rheumatoid arthritis in patients not helped by drugs designed to block an inflammation-causing protein, researchers said on Sunday.

Rituxan, currently sold as a treatment for non-Hodgkin’s lymphoma, improved arthritis symptoms by at least 20 percent in 51 percent of patients who took the drug, compared with 18 percent of patients who took a placebo, according to results from the six-month study.

The trial followed 520 patients who had not responded adequately to methotrexate and drugs such as Amgen Inc.‘s Enbrel and Abbott Laboratories’ Humira that inhibit a protein called tumor necrosis factor.

Twenty-seven percent of Rituxan patients achieved a 50 percent improvement in symptoms, compared with 5 percent on the placebo, while 12 percent achieved a 70 percent improvement, compared with 1 percent of placebo patients.

The full study results will be presented on Wednesday in San Diego at a meeting of the American College of Rheumatology.

Anti-TNF therapies are often successful in reducing joint inflammation in patients with rheumatoid arthritis, but for some patients it is not enough.

“While TNF blockers are an extremely beneficial therapy, there are patients who fail to respond or have toxicity to these therapies,” Dr. Stanley Cohen, of Radiant Research in Dallas, Texas, and an investigator in the study, said in a statement.

“For those patients, adding rituximab (Rituxan) to the treatment management plan may spell the difference in success.”

Researchers said the most common adverse effects seen in the trial were infusion-related and easily managed.

Genentech, which is majority owned by Roche Holding AG, and Biogen-Idec filed last month for U.S. regulatory approval to market Rituxan as a treatment for rheumatoid arthritis.