Abstract 992: Distinct body composition profiles in early- vs. late-onset locally advanced rectal cancer - Results from the ColoCare Study

Introduction: Muscle mass and fat distribution are key components of body composition and have been linked to treatment response, treatment toxicity, and survival in cancer patients. Few studies have investigated body composition parameters in relation with rectal cancer, with no study evaluating body composition profiles in early-onset rectal cancer (EORC; diagnosed <50 years) and late-onset rectal cancer (LORC; diagnosed ≥65 years). Methods: We utilized pre-treatment computed-tomography scans from 191 patients diagnosed with stage II/III rectal cancer recruited in Utah and Florida (two study sites of the ColoCare Study). Body composition parameters were assessed at L3 vertebral level including visceral adipose tissue (VAT), subcutaneous adipose tissue (SAT), skeletal muscle tissue (SKM), intramuscular adipose tissue (IMAT), body mass index (BMI; kg/m2; continuous), BMI categories, and sarcopenia (yes/no). Multinomial logistic regression models were used to estimate odds ratios (OR) and 95% confidence intervals (95% CI) for associations of body composition parameters with EORC and LORC, adjusted for sex, surgery, tumor stage, and study site, compared with average-onset rectal cancer (AORC;50-64 years) as the reference group. Results: Twenty-seven percent and 28% of patients were diagnosed with EORC and LORC, respectively. A one-unit increase in log-transformed IMAT area was associated with increased odds of LORC (OR 3.21 [1.46-7.08]) and decreased odds of EORC (OR 0.27 [0.13-0.59], phet=<0.05) compared to AORC. A similar pattern emerged for sarcopenia (yes/no: ORLORC 1.76 [0.86-3.62]; OREORC 0.43 [0.19-0.96], phet=0.05) and VAT: ORLORC1.03 [0.95-1.12]) and OREORC (0.91 [0.84-0.99], phet=0.01) compared to AORC. The opposite pattern and magnitude of associations was observed for a one-unit increase in log-transformed SKM (ORLORC 0.04 [0.004-0.31]; OREORC 9.49 [1.06-84.60], phet<0.05). SAT area and BMI were not associated with onset of EORC or LORC. Discussion: This study is the first analysis of a comprehensive panel of body composition parameters in EORC and LORC. LORC patients had higher IMAT or VAT areas and sarcopenia, consistent with associations in healthy older individuals. Similarly, EOCRC patients had greater SKM area, compared to AOCRC. It will be important to evaluate the associations of body composition parameters within each group with clinical outcomes and evaluate whether integrating body composition assessment into patient care may help optimize treatment response, reduce toxicities and improve outcomes. Citation Format: Mmadili N. Ilozumba, Lia Whisenant, Britton Trabert, Jeffrey T. Yap, Tengda Lin, Vaia Florou, Mark A. Lewis, Patricia A. Erickson, Nicole C. Lorona, Anita R. Peoples, Joseph Letourneau, Manju George, Sheetal Hardikar, Caroline Himbert, Maria Gomez, Biljana Gigic, Christopher I. Li, Adetunji T. Toriola, Jane C. Figueiredo, David Shibata, Erin M. Siegel, Cornelia M. Ulrich, Doratha A. Byrd, Ramya Thota, Jennifer Ose. Distinct body composition profiles in early- vs. late-onset locally advanced rectal cancer - Results from the ColoCare Study [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 992.