The dasatinib dose established in phase I will move forward to the phase II setting. If there are no DLTs, the phase II dose will be chosen based on PD parameters. Dasatinib will be administered for 28 days/cycle with rituximab 500 mg/m2 on day 1 of each cycle (375 mg/m2 on day 1 of cycle 1 only) for 6 cycles or until intolerable toxicity or disease progression. For this portion of the study, up to an additional 22 patients will be enrolled over a 6-month period for a total of 28 patients at the chosen dose level.