Body mass index and outcomes after CD19 CAR T-cell therapy for relapsed/refractory B-cell lymphoma: a nationwide registry study.

Chimeric antigen receptor (CAR) T-cell therapy is effective for treating relapsed or refractory B-cell lymphoma; however, its outcomes remain heterogeneous. We conducted a nationwide retrospective registry study in Japan to assess whether pretreatment body mass index (BMI) influences outcomes after CD19-directed CAR T-cell therapy. Among 944 patients with relapsed or refractory B-cell lymphoma treated between 2019 and 2024, BMI was categorized as Low (<18.5 kg/m²; n=166), Normal (18.5-24.9 kg/m²; n=619), or High (≥25 kg/m²; n=159). The primary endpoint was overall survival (OS). Secondary endpoints included progression-free survival (PFS), cumulative incidence of relapse or progression (CIR), non-relapse mortality, and CAR T-cell-related toxicities. Six-month OS rates in the low, normal, and high BMI groups were 73.2%, 83.7%, and 89.3%, respectively (p<0.01), and corresponding PFS was 62.3%, 75.6%, and 77.7% (p<0.01). CIR was more frequent in the Low-BMI group, whereas non-relapse mortality did not differ significantly across groups. In the overall cohort, Low-BMI was associated with shortened OS and PFS and higher CIR in multivariable analyses. In a complete-case sensitivity analysis restricted to patients with available disease status data at the time of infusion, these associations were attenuated after adjusting for disease status. Severe CAR T-cell-related toxicities were comparable across BMI groups. Pretreatment BMI may serve as a simple clinical marker associated with early outcomes after CAR T-cell therapy, although this association may be partly explained by disease status at infusion or unmeasured disease burden.