Facchinelli D, Pagano L. Progressive multifocal leukoencephalopathy during bispecific antibody therapy in multiple myeloma: from immune dysfunction to early recognition. Comment on: “Progressive multifocal leukoencephalopathy and BK virus-nephropathy with bispecific antibody therapy in multiple myeloma”. Haematologica; https://doi.org/10.3324/haematol.2026.301888 [Early view].