In phase I, patients will be enrolled in a standard "3+3" dose escalation scheme with two dasatinib cohort doses of 100 mg QD and 140 mg QD x 28 days/cycle with rituximab 500 mg/m2 on day 1 of each cycle (375 mg/m2 on day 1 of cycle 1 only). During the first cycle of each dose cohort patients will receive dasatinib on days -7 to 0 to allow for pharmacokinetic and pharmacodynamic analysis of single agent dasatinib dosing. Cohorts will be assessed for DLTs during the first 2 cycles. Treatment will continue for 6 cycles or until intolerable toxicity or disease progression. It is estimated that accrual of 3-6 patients will be completed in 4-6 months depending on DLTs observed.