Results from the pivotal- or final-stage trial found that previously untreated patients given the combination therapy had a median progression-free survival of 42.8 months, compared with 32.3 months for those on chemotherapy alone, Genentech said.

The trial involved 817 patients with chronic lymphocytic leukaemia, or CLL, the most common form of adult leukaemia.

A separate trial of 552 CLL patients who had stopped responding to chemotherapy found the combination reduced the risk of death or cancer progression by 35 per cent.

The studies, presented in San Francisco at a meeting of the American Society of Hematology, were sponsored by Genentech's majority owner Roche Holding AG, which markets Rituxan outside the United States under the brand name MabThera.

The drug, co-marketed in the United States by Genentech and Biogen Idec Inc, is approved to treat non-Hodgkin's lymphoma and rheumatoid arthritis.

Rituxan, which had US sales of US$655 million (S$997.5 million) in the third quarter, is an antibody designed to bind to a protein on the surface of B-cells where it recruits the body's natural defences to attack and kill the marked cells.

GlaxoSmithKline PLC and Genmab are developing a similar antibody, called ofatumumab. Results from a smaller Phase 3 trial of that drug in CLL patients who have stopped responding to chemotherapy will be presented at the haematology conference on Monday. -- REUTERS