At the Crossroads of Lineage: Secondary Malignancies After CAR-Based Immunotherapy.

CD19-directed chimeric antigen receptor (CAR) T-cell therapies have been instrumental in improving outcomes of refractory or relapsed B-cell malignancies. However, there have been safety concerns due to recent reports of second primary malignancies (SPMs) related to CAR T-cell therapies. We reviewed articles from Embase, PubMed, and Cochrane Library records and included SPM case reports as well as cohort studies. Across published cohorts, secondary cutaneous or peripheral T-cell lymphoma (PTCL) after diffuse large B-cell lymphomas (DLBCLs) have been reported at low incidence (generally in the low single-digit percentage range). While CAR T-cell therapy is associated with these rare secondary malignancies and lineage-switch events primarily described in acute leukemia, they are clinically significant and have resulted in increased surveillance. The currently available evidence suggests that most secondary malignancies after CAR T-cell therapy are due to background risk and prior treatment exposures rather than direct CAR T-cell therapy induced oncogenesis. However, rare CAR T-cell therapy-associated second primary T-cell malignancies have been reported. To properly define incidence, mechanisms, and risk factors for CAR T-cell therapy-associated malignancies, continued prospective registry follow-up and additional research will be needed.