Beyond BMI: Roles of SPISE, Central Adiposity and Body Composition in Pediatric Brain Tumor Survivors

Background/Objectives. Pediatric brain tumor survivors (PBTS) are at increased risk of cardiometabolic complications due to tumor- and treatment-related hypothalamic–pituitary (HP) damage and adverse body composition. We evaluated associations of the Single-Point Insulin Sensitivity Estimator (SPISE) with central adiposity, DXA-derived body composition, metabolic abnormalities, and HP involvement. Methods. In this retrospective study, 119 PBTSs (median age, 12.7 years; median time since therapy, 2.4 years) were evaluated. SPISE, BMI, waist-to-height ratio (WHtR), DXA-derived fat-to-lean ratio (FLR), and metabolic syndrome (MetS) were assessed. Multivariable logistic regression evaluated the association between SPISE and central adiposity. Exploratory receiver operating characteristic analyses compared the discriminatory performance of SPISE, BMI-SDS, HOMA-IR, and FLR. Results. Central adiposity was present in 58.8% of participants, whereas BMI-defined obesity occurred in 21.8%. Lower SPISE values were associated with central adiposity, obesity, MetS, HP damage, and multiple pituitary hormone deficiencies (all p < 0.05). SPISE declined across pubertal stages and remained associated with central adiposity after adjustment for age and selected HP variables (OR = 0.58, 95% CI 0.46–0.73). SPISE showed good discrimination of central adiposity (AUC = 0.81), with an exploratory, cohort-derived threshold of 7.82; FLR provided complementary information on body composition. Conclusions. Central adiposity was common and not fully captured by BMI-defined obesity. Lower SPISE values were associated with concurrent anthropometric and metabolic abnormalities, while DXA-derived FLR added descriptive information on body composition. Whether these indices improve cardiometabolic risk stratification beyond conventional measures requires prospective investigation.