Immune Effector Cell‐Associated Hematotoxicity With Secondary Myelofibrosis Following Idecabtagene‐Vicleucel for Multiple Myeloma, Comprehensively Treated With Autologous Hematopoietic Stem Cell Boosting

Pancytopenia accompanied by chimeric antigen receptor T cell (CAR‐T) therapy is termed immune effector cell‐associated hematopoietic toxicity (ICAHT), which is often sustained and refractory to supportive care. We report a case of a 52‐year‐old man with multiple myeloma who developed severe ICAHT with secondary myelofibrosis (sMF) after administration of idecabtagene‐vicleucel, which was comprehensively improved by autologous hematopoietic stem cell boosting. This case focuses on sMF as a rare but cautionary complication of CAR‐T therapy, underscoring the importance of bone marrow biopsy to exclude sMF and of stem cell boosting for the treatment of persistent ICAHT.