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

Background: Rituximab is a chimeric monoclonal antibody directed against th e B-cell CD20 antigen which has been utilized for therapy of B-cell non-Hod gkin'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 treatm ent, an open-label, single-arm, multi-center, phase II study of eight conse cutive 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 wa s conducted. Thirty-seven patients with a median age of 55 years were treat ed. Results: Grade 1 or 2 adverse events were the majority of reported toxiciti es and occurred most frequently with the first infusion, decreasing with su bsequent infusions. No patients developed a host antibody response (HACA) t o Rituximab. The mean serum immunoglobulin levels for IgG, IgA, and IgM sta yed within the normal range throughout the study. The majority of patients who were bcl-2 positive at baseline in peripheral blood became bcl-2 negati ve during treatment and remained negative at the time of B-cell recovery. I n 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 eval uable patients, 21 (60%) responded to treatment (14% CR and 46% PR). In res ponders, the median time to progression (TTP) and the median response durat ion have not been reached after 19.4+ months and 13.4+ months, respectively . Conclusions: The safety profile and efficacy achieved in this pilot study o f extended treatment with Rituximab compares favorably with that seen with four weekly doses. Further studies are warranted to investigate whether thi s or other extended Rituximab schedules will result in increased efficacy i n all or in certain subgroups of patients with low-grade or follicular NHL.