Kaplan-Meier estimates of time to tumor progression (days) of lymphoma cells (Ramos) in inoculated mice. Athymic mice (8 mice per group) were inoculated subcutaneously with 7 × 10⁶ Ramos (Burkitt lymphoma) cells. Seventy-two hours after inoculation, mice were randomly assigned to treatment with 4HPR (250 μg/d, 5 days per week), rituximab (200μg/wk), 4HPR + rituximab (at the same doses), or solvent only (negative control) for 4 weeks.