Impact of Body Weight Loss During Preoperative Chemoradiotherapy on Prognosis of Patients With Lower Rectal Cancer

Background Preoperative chemoradiotherapy is the standard treatment for locally advanced rectal cancer (LARC), but may cause body composition changes. The prognostic impact of these changes remains unclear. The present study investigated the relationship between changes in body weight and composition during chemoradiotherapy, such as the psoas muscle mass index, visceral fat index, and subcutaneous fat index (SFI) obtained from computed tomography images, and long‐term outcomes in LARC patients. Methods This retrospective study included 343 patients with LARC treated with preoperative chemoradiotherapy followed by curative resection between 2005 and 2023 at our hospital. Changes in body composition during chemoradiotherapy were retrospectively assessed, and the relationship between each index and long‐term outcomes was examined. Results Forty‐one patients had body weight loss ≥ 10% during chemoradiotherapy, which correlated with reductions in 5‐year overall survival (OS) (68.2% vs. 90.5%, p < 0.001) and disease‐free survival (DFS) (53.5% vs. 70.9%, p = 0.005) rates. SFI loss ≥ 22.0% was also associated with a lower 5‐year OS rate (74.3% vs. 88.3%, p < 0.001). A multivariate analysis identified body weight loss ≥ 10% (HR 2.98, p = 0.001) and SFI loss ≥ 22.0% (HR 2.84, p = 0.007) as independent predictors of worse OS. Body weight loss ≥ 10% was also independently associated with worse DFS (HR 1.79, p = 0.014). Pre‐chemoradiotherapy body mass index ≥ 25 kg/m 2 and the cT4 factor had high odds ratios for body weight loss ≥ 10% during chemoradiotherapy. Conclusion Body weight loss during preoperative chemoradiotherapy is an independent predictor of worse OS and DFS in LARC.