Abnormal bone marrow findings in patients following treatment with chimeric antigen receptor‐T cell therapy.

Background: Bone marrow (BM) assessment after CAR‐T cell immunotherapy infusion is not routinely performed to monitor adverse events such as cytopenias, hemophagocytic lymphohistiocytosis, or infections. Our institution has performed BM biopsies as part of CAR‐T cell treatment protocols, encompassing pre‐ and post‐treatment time points and during long‐term follow‐up. Methods: We conducted a systematic retrospective review of BM abnormalities observed in samples from 259 patients following CAR‐T cell immunotherapy. We correlated BM pathology findings with mortality, relapse/residual disease, and laboratory values. Results: At a median of 35.5 days post‐CAR‐T infusion, 25.5% showed severe marrow hypocellularity, and 6.2% showed serous atrophy, and peripheral blood cytopenias corroborated these observations. Marrow features associated with reduced disease burden post‐CAR‐T infusion include increased lymphocytes seen in 16 patients and an increase of macrophages or granulomatous response seen in 25 patients. However, a 100‐day landmark analysis also showed increased marrow histiocytes were associated with lower survival (median OS 6.0 vs. 21.4 months, p =.026), as was grade 2–3 marrow reticulin (18 patients) (median OS 12.5 vs. 24.2 months, p =.034). Conclusions: These data represent the first systematic observations of BM changes in patients receiving CAR‐T cell immunotherapy. [ABSTRACT FROM AUTHOR]