Genentech ( DNA) and Biogen Idec ( BIIB) are asking the Food and Drug Administration to expand the use of the lymphoma drug Rituxan. The biotech companies have submitted a supplemental biologics license application to seek approval of the drug as a first-line treatment for previously untreated patients with low-grade or follicular, CD20-positive, B-cell non-Hodgkin's lymphoma in combination with chemotherapy. They're also pursuing clearance to have Rituxan used after a chemo regimen of cyclophosphamide, vincristine and prednisone in patients whose disease has been stabilized or improved. Rituxan is already prescribed as a stand-alone treatment for patients with relapsed or refractory, low-grade or follicular CD20-positive, B-cell non-Hodgkins. Rituxan in combination with two chemo regimens was approved in February as a first-line treatment for patients with diffuse large B-cell lymphoma. That same month, Rituxan was given the green light to be used with methotrexate to reduce the symptoms of rheumatoid arthritis. An estimated 360,000 Americans have non-Hodgkin's lymphoma, and more than 58,000 new cases are diagnosed each year. About half of the patients have a slow-growing but usually incurable form of the disease. The most common type is called follicular lymphoma. The other half have a faster-growing disease that multiplies rapidly in the body, and if left untreated it can be fatal. Shares of Genentech, the world's biggest biotech measured by market cap, were down 61 cents, or 0.7%, to $83.78. Biogen Idec was higher by 17 cents, or 0.4%, at $47.39.