Association between systemic immune-inflammatory index and body mass index in cancer patients: A cross-sectional study from NHANES 2013 to 2018.

A novel integrative biomarker, the systemic immune-inflammatory index (SII), has been understudied in cancer research. This study aimed to examine potential associations between body mass index (BMI) and SII in cancer patients. It included cancer patients aged 20 to 79 from the National Health and Nutrition Examination Survey (NHANES) conducted between 2013 and 2018. A cross-sectional analysis comparing SII and BMI was performed using EmpowerStats software (version 3.4.3) and R packages. We utilized multivariate regression analysis to examine the association between SII and BMI in cancer patients. To further explore the relationship between the 2, we employed threshold effect analysis, stratified analysis, and smoothed curve fitting. The study included 1067 cancer patients, with a mean SII value of 553.32 ± 390.44. Our multivariate regression analysis revealed a positive association exists between BMI and SII in the fully adjusted model, with this relationship observed across all 3 groups. The threshold value between log-transformed SII (lgSII) and BMI, as identified by the segmented linear regression model, was 3.04 (×103 cells/μL). However, no inflection point was observed in female patients following stratification by gender. Our findings suggest that SII may reflect the systemic inflammatory status associated with obesity. However, its predictive value requires further validation in prospective studies.