Differential Association of Visceral and Subcutaneous Adipose Tissue with Treatment Response to Neoadjuvant Chemoradiotherapy in Locally Advanced Rectal Cancer

Background: In locally advanced rectal cancer, neoadjuvant concurrent chemoradiotherapy (CCRT) followed by surgery is the standard treatment. Pathologic complete response (pCR) is strongly associated with favorable long-term outcomes; however, reliable pre-treatment biomarkers for predicting treatment response remain limited. This study aimed to investigate the association between CT-derived adipose tissue parameters and pathologic response following neoadjuvant CCRT. Methods: A total of 61 patients with locally advanced rectal cancer who underwent neoadjuvant CCRT followed by surgery between 2020 and 2024 were retrospectively analyzed. Visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) parameters, including area, index, and mean attenuation (Hounsfield unit, HU), were measured at the L3 level on pre-treatment CT. Patients were classified into favorable (complete or near-complete response) and unfavorable response groups, as well as response and no-response groups. Statistical analyses included independent t-tests, chi-square tests, and receiver operating characteristic (ROC) curve analysis. Results: In the favorable versus unfavorable response analysis, higher body mass index (BMI), larger VAT area, higher VAT index (VATI), and lower mean VAT attenuation were significantly associated with favorable response (all p < 0.05), whereas SAT-related parameters were not. In the response versus no-response analysis, SAT area and SAT index (SATI), but not mean SAT attenuation and VAT-related parameters, were significantly associated with treatment response (all p < 0.05). BMI was significantly associated with pathologic response only in the favorable versus unfavorable response group analysis, whereas no significant association was observed in the response versus no-response group analysis. Conclusions: CT-derived adipose tissue parameters were differentially associated with pathologic response to neoadjuvant CCRT in locally advanced rectal cancer. VAT parameters, including both quantity and attenuation, were associated with favorable response, whereas SAT parameters were associated with overall treatment response, suggesting compartment-specific roles of adipose tissue in modulating treatment outcomes. While BMI demonstrated a significant association in one subgroup analysis, CT-based body composition analysis may provide more comprehensive and compartment-specific information beyond conventional anthropometric measures, and may serve as a potential imaging biomarker for predicting treatment response.