Progressive multifocal leukoencephalopathy, advanced ductal breast carcinoma, systemic sclerosis, and checkpoint inhibitors: a therapeutic dilemma.

Progressive multifocal leukoencephalopathy (PML) is a demyelinating central nervous system disease infection by JC virus (JCV) in patients with a significant decline in cellular immunity. No specific treatment has demonstrated efficacy, and the disease progresses to death in most patients. Recent findings have shown stabilization or improvement of PML lesions after treatment with checkpoint inhibitors (CPI) based on immune reconstitution. Nevertheless, immunotherapy may specifically cause autoimmune diseases or may deteriorate pre-existing ones. We report a case of a patient under treatment for advanced ductal breast carcinoma and systemic sclerosis, who developed PML. The therapeutic approach included withdrawal of drugs with possible immunosuppressive effect and treatment with pembrolizumab. In the absence of reliable markers to predict CPIs response and a concern for an autoimmune worsening, immunotherapy was administered late in the course of the disease. Finally, she did not experience an autoimmune disease flare-up; however, pembrolizumab could not prevent disease progression. We believe that potential autoimmune complications should not delay treatment initiation with CPIs in PML.