Underweight <scp>BMI</scp> Independently Predicts Inferior Survival in <scp>DLBCL</scp> Treated With R‐ <scp>CHOP</scp> : A Lymphoma Registry Study

OBJECTIVES: BMI may capture clinically relevant differences in host reserve and treatment vulnerability in diffuse large B-cell lymphoma (DLBCL). We evaluated the association between BMI and survival outcomes. METHODS: Adults with DLBCL receiving first-line R-CHOP chemoimmunotherapy from 2016 to 2026 were identified from the Lymphoma and Related Diseases Registry. BMI was analysed as underweight, normal weight/overweight, obese Class I and obese Class II/III. Overall survival (OS) and progression-free survival (PFS) were analysed using Kaplan-Meier and Cox models adjusted for International Prognostic Index (IPI) components, sex and cardiac history. RESULTS: Among 1600 patients, 43 (2.7%) were underweight, 303 (18.9%) had obese Class I BMI and 198 (12.4%) had obese Class II/III BMI. At median follow-up of 35.4 months, 342 deaths occurred, including 15 in underweight patients. OS differed by BMI category (log-rank p = 0.017), whereas PFS did not (log-rank p = 0.082). In complete-case multivariable analysis, underweight BMI remained associated with inferior OS (adjusted HR, 1.89; 95% CI, 1.06-3.37). Exploratory analyses did not identify chemotherapy exposure, including upfront dose reduction, or measured malnutrition/systemic illness markers that explained this association. CONCLUSIONS: Underweight BMI identified patients at increased risk of inferior survival, even after adjustment for IPI-based prognostic factors. Obese BMI categories were not associated with inferior survival.