A trial of Roche Holding's <ROG.VX Rituxan found that use of the drug in patients with a type of slow-growing lymphoma significantly delayed the need for chemotherapy treatment.

The typical practice for patients with such advanced-stage follicular lymphoma has been a watchful-waiting approach in which use of chemotherapy, which causes debilitating side effects, is delayed until the cancer progresses.

Of the 60,000 or so cases of non-Hodkgin's lymphoma diagnosed in the United States each year, about one quarter are "indolent," said Sandra Horning, head of hematology/oncology clinical development at Roche's Genentech unit. About 40 percent of those cases fall into the "watch and wait" category, she said.

Follicular lymphoma is a slow-developing but incurable form of non-Hodgkin's lymphoma. It is one of the most common types of lymphoma, which is a cancer of the lymphatic system.

The Rituxan trial found that after three years, 49 percent of patients in the watchful-waiting arm had not required new therapy, while 80 percent of patients treated for a short period with Rituxan and 91 percent of patients treated periodically with the drug had not required new therapy.

Researchers, who presented the study results in Orlando, Florida, on Sunday at a meeting of the American Society of Hematology, said 96 percent of patients in the study remain alive, and there is no difference in overall survival between the three arms.

Rituxan, first approved in 1997, is currently marketed for treating non-Hodgkin's lymphoma, rheumatoid arthritis and chronic lymphocytic leukemia. Sales last year totaled 6.1 billion Swiss francs, or about $5.6 billion.

The drug, given by infusion, is an antibody that binds to a specific protein, CD20, found on the surface of malignant and normal B-cell lymphocytes, enlisting the body's own immune system to kill marked cells.

Results from an earlier-stage trial of Roche's third generation anti-CD20 antibody, an experimental drug known as GA101, were slated for presentation at the hematology meeting later on Sunday.

Horning said the new molecule has more direct cell-killing power than Rituxan.