LONDON (Reuters) - Lymphoma patients who continue regular infusions of Genentech Inc and Biogen Idec's Rituxan after chemotherapy may live longer than patients who stop, Israeli researchers said on Tuesday.

They found patients who stayed on so-called maintenance therapy with the drug, also known as rituximab or MabThera, were 40 percent more likely to be alive after three years compared with those who stopped.

Studies have shown that the drug combined with chemotherapy helps people live longer. But less clear have been the benefits of continuing with regular infusions of Rituxan, which can raise the chances of infection, they said.

Rituximab is a monoclonal antibody, a genetically-engineered immune system molecule designed to suppress the immune system in cancer and rheumatoid arthritis. Roche sells the drug as MabThera in Europe.

"Our results suggest that rituximab maintenance therapy for up to two years ... should be added to standard therapy of patients with relapsed or refractory follicular lymphoma after successful induction treatment," Liat Vidal and colleagues at the Rabin Medical Center in Petah-Tivka, Israel wrote.

"The higher rate of infections with rituximab therapy should be taken into consideration when making treatment decisions."

Follicular lymphoma is the second most common of the several types of non-Hodgkin lymphoma, a cancer of the lymphatic system. The usual treatment is a chemotherapy cocktail but patients often relapse years afterwards.

These people usually receive a high dose of chemotherapy to kill the lymphoma cells and then get a bone marrow stem cell transplant. But this also shuts down the blood-producing stem cells, leaving people vulnerable to infection.

Vidal and colleagues pooled data from five randomised trials involving 985 people to compare the effects of continuing Rituxan infusions after chemotherapy with stopping the drug after chemotherapy.

Patients who remained on the drug had a 40 percent improvement in overall survival, they reported in the Journal of the National Cancer Institute. This means that these people were more likely to be alive after three years, Liat Vidal, who led the study, said in a telephone interview.

The benefit was statistically significant for people with relapsed lymphoma but not for previously untreated patients, the researchers said.

At the same time people continuing with Rituxan had nearly twice the rate of infection-related problems when compared with those who stopped receiving the drug.

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