Effect of in vivo caspase inhibition on tumor growth in palpable FL-18 xenografts. Palpable FL-18 tumors were established in athymic mice (5 mice per group). Mice were then treated with control (diluent only), 4HPR (250 μg/d, 5 days per week) + rituximab (200 μg/wk + irreversible pan caspase inhibitor Q-VD(OMe)-Oph (200 μg/d ip for 5 days a week), or 4HPR + rituximab (at doses above) without Q-VD(OMe)-Oph. Tumor volume in mm³ (y-axis) was measured over time (x-axis). Error bars indicate standard deviation.