Progressive multifocal leukoencephalopathy in patients with follicular lymphoma treated with bendamustine plus rituximab followed by rituximab maintenance

Progressive multifocal leukoencephalopathy (PML) is a rare fatal disease caused by polyomavirus JC occurring in the context of a deep and prolonged immunosuppression. Rituximab is one of the monoclonal antibodies labelled with a black box warning for the risk of PML. The estimated incidence rate of PML ranges from 1·39 to 1·87 per 10·000 rituximab‐exposed patients (Focosi et al., 2019). Although PML is classified as a ‘very rare’ complication of rituximab treatment, the combination with other drugs may significantly modify this risk. In the last decade, the combination of bendamustine and rituximab (BR) has become the preferred regimen chosen by many hematologists to treat patients with high tumour burden follicular lymphomas (FL). Similarly, maintenance therapy administering rituximab every two or three months for two years has become part of standard first line treatment of FL. Here we report our monocentric experience of three cases of PML occurring in patients with FL treated with BR followed by rituximab maintenance.