Incidence of Progressive Multifocal Leukoencephalopathy in Non-Hodgkin Lymphoma Patients Treated with Rituximab.

Abstract 3675

Poster Board III-611

Progressive multifocal leukoencephalopathy (PML) is a rare complication of immunesuppression due to productive reactivation of JC polyomavirus (JCV) in glial cells. In the last decades many case reports of rituximab-associated PML have raised concerns, but no systematic incidence rate analysis has been ever performed. We retrospectively reviewed our clinical records with the aim of calculating the incidence rate of PML in patients with NHL who had been treated with regimens including rituximab. Data on HIV-negative patients who received the first dose of rituximab from January 1, 2000 to June 30, 2008, were analyzed. The follow-up period was from the first rituximab dose to the last recorded visit, up to September 30, 2008. PML cases were included if symptoms occurred at least 1 month after the first dose of rituximab and the diagnosis was supported by magnetic resonance imaging and detection of JCV DNA in stereotactic brain biopsies and/or cerebrospinal fluid. We collected data from 821 consecutive patients throughout the follow-up period. All patients received chemotherapy other than rituximab, and all completed their entire treatment course at the Hematology Unit in Pisa. No radiation therapy was administered. The median time of follow-up was 20 months (range = 1-106 month), resulting in 1725 patient-years at risk. Five cases of PML (two receiving maintenance rituximab) were identified, with an incidence rate of 2.89 cases per 1000 patient-years. We found that the incidence rate of PML in our population exceeded that observed in patients who are traditionally regarded as being at high risk of PML, namely patients with B-cell chronic lymphocytic leukaemia and AIDS. Rituximab might be a potential contributing factor to the development of PML in these patients. Nevertheless, rituximab currently represents an essential therapeutic tool that can positively affect the natural history of NHL. However, because of the expanding therapeutic indications, it seems reasonable to investigate the potential contribution of rituximab to PML occurrence.