Malignancies after Chimeric Antigen Receptor T Cell Therapy

CAR-T cell therapy is a transformative treatment for relapsed and/or refractory (R/R) B cell non-Hodgkin lymphoma (NHL), B cell acute lymphoblastic leukemia (ALL), chronic lymphocytic leukemia (CLL), and multiple myeloma (MM). Recent data brought serious concerns for the development of second primary malignancies (SPM), whether second myeloid neoplasms (SMN) or second non-hematologic malignancies (SNHM), or T cell cancers. Pertaining SPMs after CAR-T cell therapy, studies report an incidence ranging from 2.3% to 11.3%, with a higher trend in patients 65 years of age or older, those with higher number of prior therapies, and those with longer follow-up. In the case of SMNs, myelodysplastic syndrome is the most common, ranging from 0.3% to 4.2%, followed by acute myeloid leukemia in 0.2% to 1.1% of cases. In SNHM, the incidence ranges from 0.6% to 11.6% and does not appear limited to a particular diagnosis or CAR-T cell product. Establishing a causal association between CAR-T cell therapy and development of T cell malignancies is challenging. Notwithstanding the possibility of underreporting, the incidence of T cell cancers after commercially approved CAR-T cell therapies ranges from 0.03% to 1%, occurring at 1 to 36 months postinfusion, with only a handful of reports confirming CAR transgene integration. We believe that therapeutic benefits of CAR-T cell therapies in R/R B cell NHL, B cell ALL, CLL, and MM outweigh their potential risks of developing SPMs and T cell cancers. More work is needed to help better understand the corresponding contributions of CAR-T cell therapy per se as opposed to other factors, including pre-existing somatic or germline mutations, chemotherapy- and/or radiotherapy-acquired clonal hematopoiesis, and their ultimate effect on developing SPMs.