Bispecific antibody therapy in multiple myeloma and risk of progressive multifocal leukoencephalopathy

Context: Bispecific antibodies (bsAbs) recently reshaped the treatment landscape of multiple myeloma (MM). Rare cases of progressive multifocal leukoencephalopathy (PML) have been reported in MM patients, and more recently in bsAbs-treated patients. Objectives: We aimed to investigate a potential safety signal for PML in patients with MM treated with bsAbs. Methods: We included all patients with MM treated with bsAbs identified in the French prospective registry of JC polyomavirus infections of the central nervous system and/or from the French pharmacovigilance database (FPVD). We also performed a systematic review. We then assessed whether a disproportionality signal for PML reporting exists, comparing bsAbs and other MM therapies in VigiBase®, the world pharmacovigilance database. Results: In the registry-FPVD cohort, 14 patients were included; all had at least triple-refractory MM, with a median disease duration of 13 years (IQR, 10-14) and were exposed to BCMA-targeting bsAbs (median time to PML diagnosis: 22 months, IQR, 12-24); 10 (71%) were in complete response. Main clinical manifestations included motor deficit, cognitive impairment and visual symptoms (8/14 patients each, 57%). Twelve (86%) had died from PML by month 12. Similar features and outcomes were observed in the systematic review (n=14 cases). PML reporting was significantly higher with bsAbs than with other MM therapies (Reporting Odds Ratio 17.7; 95% CI, 12.1-26.1). Interpretation: PML may represent an emerging complication in patients with MM receiving bsAbs. Vigilant monitoring and rapid assessment of new neurological deficits are critical in this population.