Patients and Methods: Five hundred seventy-one patients with previously untreated stage III or IV low-grade non-Hodgkin's lymphoma were registered. Patients received six to eight cycles of prednisone, methotrexate, doxorubicin, cyclophosphamide, and etoposide/mechlorethamine, vincristine, procarbazine, and prednisone (ProMACE[day 1]-MOPP[day 8]) chemotherapy or chemotherapy plus radiotherapy. Responding patients were randomized to observation alone or to interferon consolidation. Interferon alfa-2b 2 mU/m(2) was given subcutaneously three times weekly for 2 years.

Results: Two hundred sixty-eight eligible patients were randomized to interferon alfa consolidation (n = 144) or observation alone (n = 124). With a median follow-up time from randomization among patients still alive of 6.2 years, the median PFS time wets 4.1 years for patients who received interferon consolidation therapy and 3.2 years for patients who were observed after PraMACE-MOPP induction (P =.25). The adjusted hazard ratio for relapse for observation to interferon was 0.83 (95% confidence interval [CI], 0.61 to 1.13). The median OS has not been reached in either group. At 5 years, OS is 78% for the interferon group and 77% for the observation group (P =.65). The adjusted hazard ratio for survival for observation to interferon is 1.11 (95% CI, 0.69 to 1.79).

Conclusion: Interferon alfa consolidation therapy after intensive treatment with anthracycline-containing combination chemotherapy and involved-field radiation therapy does not prolong the PFS or OS of patients with low-grade non-Hodgkin's lymphoma. J Clin Oncol 18:2010-2016. (C) 2000 by American Society of Clinical Oncology.