Radioimmunotherapy consolidation using 131I-tositumomab for patients with chronic lymphocytic leukemia or small lymphocytic lymphoma in first remission.

Despite initial responses to chemoimmunotherapy, relapse and minimal residual disease (MRD) remain major issues in treatment of chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma (SLL) patients. We administered (131)I-tositumomab to patients in complete response (CR) or partial response (PR) after induction chemotherapy. Toxicities and rate of PR to CR conversion and MRD elimination were assessed three months later. The study stopped prematurely after enrolling 16 patients. Four (25%) were in CR, 12 (75%) in PR, and 12 (75%) had MRD. Three months after treatment with (131)I-tositumomab, CR was achieved (n = 8; 50%) or sustained (n = 4; 25%) in 12 patients and MRD was eliminated in four of 12 patients (33%). Hematologic toxicities were anemia in one patient (6%), neutropenia in 13 (81%), and thrombocytopenia in eight (50%). Two patients (12%) developed MDS 17 and 20 months after consolidation. Consolidation with (131)I-tositumomab for CLL/SLL patients in first remission is feasible and may provide the benefit of converting PR to CR and/or eliminating MRD.