Pentostatin, cyclophosphamide, and rituximab (PCR)* therapy: Patients receive pentostatin IV over 10-30 minutes, cyclophosphamide IV over 30-60 minutes, and rituximab** IV on day 1. Patients also receive filgrastim (G-CSF) subcutaneously (SC) beginning on day 3 or pegfilgrastim SC on day 1 and continuing until blood counts recover. Treatment repeats every 28 days for a total of 6 courses in the absence of unacceptable toxicity.