Efficacy of 4HPR and rituximab in tumor killing using a palpable B-cell lymphoma xenograft model. Palpable DHL-4 (A) and FL-18 (B) tumors were established in athymic mice a median of 18 days after inoculation (5 mice per group). Mice were then treated with 4HPR (250 μg/d, 5 days per week), rituximab (200 μg/wk, 4HPR + rituximab (at the noted doses), or no drug (solvent only) for 4 weeks. Tumor volume in mm³ (y-axis) was measured over time (x-axis). Curves were truncated when mice required humane killing because of tumor progression. Error bars indicate standard deviation.