Extended Rituximab (anti-CD20 monoclonal antibody) therapy for relapsed or refractory low-grade or follicular non-Hodgkin's lymphoma

Background: Rituximab is a chimeric monoclonal antibody directed against the B-cell CD20 antigen which has been utilized for therapy of B-cell non-Hodgkin's lymphoma. A previous clinical trial demonstrated that treatment with four weekly doses of 375 mg/m(2) of Rituximab in patients with relapsed or refractory low-grade or follicular B-cell non-Hodgkin's lymphoma (NHL) was well tolerated and had significant clinical activity. Patients and methods: To assess the safety and efficacy of Rituximab treatment, an open-label, single-arm, multi-center, phase II study of eight consecutive weekly infusions of 375 mg/m(2) Rituximab in patients with low-grade or follicular B-cell NHL who had relapsed or had failed primary therapy was conducted. Thirty-seven patients with a median age of 55 years were treated. Results: Grade 1 or 2 adverse events were the majority of reported toxicities and occurred most frequently with the first infusion, decreasing with subsequent infusions. No patients developed a host antibody response (HACA) to Rituximab. The mean serum immunoglobulin levels for IgG, IgA, and IgM stayed within the normal range throughout the study. The majority of patients who were bcl-2 positive at baseline in peripheral blood became bcl-2 negative during treatment and remained negative at the time of B-cell recovery. In the 37 intent-to-treat patients, 5 (14%) had a complete response and 16 (43%) had a partial response for an overall response rate of 57%. Of 35 evaluable patients, 21 (60%) responded to treatment (14% CR and 46% PR). In responders, the median time to progression (TTP) and the median response duration have not been reached after 19.4+ months and 13.4+ months, respectively. Conclusions: The safety profile and efficacy achieved in this pilot study of extended treatment with Rituximab compares favorably with that seen with four weekly doses. Further studies are warranted to investigate whether this or other extended Rituximab schedules will result in increased efficacy in all or in certain subgroups of patients with low-grade or follicular NHL.