Prolonged Cytopenia After Idecabtagene Vicleucel for Multiple Myeloma is Associated with Poor Overall Survival

Cytopenias are well-recognized toxicities of idecabtagene vicleucel (ide-cel), a chimeric antigen receptor T cell (CAR-T) therapy approved for the treatment of relapsed, refractory multiple myeloma (RRMM). However, little is known of prognostic implications of cytopenias that persist 30 to 100 days after CAR-T infusion. We report the duration, incidence, and impact on outcomes of post-CAR-T cytopenias at Day 30 and Day 100, defined as an absolute neutrophil count of <500 cells/mm³ and/or platelet count <20 × 10⁹ cells/L, per the recent definitions of immune effector cell-associated hematotoxicity for neutropenia (N-ICAHT) and thrombocytopenia (T-ICAHT). Using observational data from the Center for International Blood and Marrow Transplant Research, we identified 821 patients treated during 2021 to 2023. The cumulative incidence of cytopenias at Day 30 was 25% and at Day 100 was 2%. Patients with Day 30 cytopenias had inferior progression-free survival (PFS) (39% versus 45%, P = .01) and overall survival (OS) at 12 months (57% versus 76%, P < .01). While there was no significant difference in PFS in patients who had Day 100 cytopenias (42% versus 53%, P = .12), compared to those who did not, patients with Day 100 cytopenias had significantly inferior OS at 12 months (55% versus 82%, P < .01). High (≥2) chimeric antigen receptor cell-mediated hematotoxicity score was associated with cytopenias at Day 30 (hazard ratio 5.26, P < .001). Cytopenias at Day 30 after ide-cel were associated with inferior PFS and OS. In addition, cytopenias at Day 100 after ide-cel are rare and are associated with inferior OS.