Multicenter phase 2 trial of rituximab for Waldenström macroglobulinemia (WM): an Eastern Cooperative Oncology Group Study (E3A98).

Waldenström macroglobulinemia (WM) is a low-grade lymphoplasmacytic lymphoma that strongly expresses CD20 on the cell surface. This study was undertaken to determine the response rate of patients with untreated or previously treated WM to the monoclonal antibody rituximab, which is directed against CD20+ expressed by B-cell lymphomas. Thirty-four untreated and thirty-five previously treated patients received rituximab 375 mg/m2 weekly for 4 consecutive weeks by intravenous infusion on days 1, 8, 15, and 22. Sixty-nine patients were evaluable for response; 19 (27.5%) achieved an objective response and 17 (24.6%) achieved a minor response. The overall response rate was 52.2% (90% CI [41.6%, 62.6%]). Of previously untreated patients 35.3% vs. 20% of previously treated patients achieved an objective response. Median response duration was not significantly different between previously untreated (27 months) and previously treated patients (not reached, P = 0.8). Rituximab produced objective or minor responses in 52.2% of patients and is an active agent in the treatment of WM. Grade 4 toxicity was seen in 11%.