Influence of skeletal muscle and intermuscular fat on postoperative complications and long-term survival in rectal cancer patients

Abstract

Background: The body composition of patients with rectal cancer potentially affects postoperative outcomes. This study explored the correlations between skeletal muscle and adipose tissue quantified by computed tomography (CT) with postoperative complications and long-term prognosis in patients with rectal cancer after surgical resection.

Methods: This retrospective cohort study included patients with rectal cancer who underwent surgical resection at the Wuhan Union Hospital between 2014 and 2018. CT images within 3 months prior to the surgery were used to quantify the indices of skeletal muscle and adipose tissue at the levels of the third lumbar vertebra (L3) and umbilicus. Optimal cut-off values for each index were defined separately for males and females. Associations between body composition and postoperative complications, overall survival (OS), and disease-free survival (DFS) were evaluated using logistic and Cox proportional hazards models.

Results: We included 415 patients (240 males and 175 females; mean age: 57.8 ± 10.5 years). At the L3 level, a high skeletal muscle density (SMD; hazard ratio [HR]: 0.357, 95% confidence interval [CI]: 0.191-0.665, P = 0.001; HR: 0.571, 95% CI: 0.329-0.993, P = 0.047) and a high skeletal muscle index (SMI; HR: 0.435, 95% CI 0.254-0.747, P = 0.003; HR: 0.568, 95% CI: 0.359-0.897, P = 0.015) were independent prognostic factors for better OS and DFS. At the umbilical level, a large intermuscular fat area (IMFA; HR: 1.904, 95% CI: 1.068-3.395, P = 0.029; HR: 2.064, 95% CI: 1.299-3.280, P = 0.002) was an independent predictive factor for worse OS and DFS, and a high SMI (HR: 0.261, 95% CI: 0.132-0.517, P < 0.001; HR: 0.595, 95% CI: 0.387-0.913, P = 0.018) was an independent prognostic factor for better OS and DFS. The models combining body composition and clinical indicators had good predictive abilities for OS. The receiver operating characteristic areas under the curve were 0.848 and 0.860 at the L3 and umbilical levels, respectively (both P < 0.05).

Conclusions: No correlations existed between CT-quantified body composition parameters and postoperative complications. However, a high SMD and high SMI were significantly associated with longer OS and DFS at the L3 level, whereas a large IMFA and low SMI were associated with worse OS and DFS at the umbilical level. Combining CT-quantified body composition and clinical indicators could help physicians predict the prognosis of patients with rectal cancer after surgery.

Keywords: Disease‐free survival; Intermuscular fat; Overall survival; Postoperative complications; Rectal cancer; Skeletal muscle density; Skeletal muscle index.

Figure 1

Body morphometric evaluations of abdominal fat and muscle areas at the L3 level and umbilical level. Axial slices of a male patient at the L3 and umbilical levels. (A) Sagittal reformation of a preoperative CT scan at the L3 level. (B, C) skeletal muscle area (in red) is 96.32 cm²; intermuscular fat area (in yellow) is 4.08 cm²; visceral fat area (in blue) is 47.26 cm²; subcutaneous fat area (in green) is 102.40 cm². (D) Sagittal reformation on preoperative CT scan at the umbilical level. (E, F) skeletal muscle area (in red) is 96.12 cm²; intermuscular fat area (in yellow) is 4.27 cm²; visceral fat area (in blue) is 56.09 cm²; subcutaneous fat area (in green) is 148.20 cm². CT, computed tomography; L3, lumbar 3 vertebra.

Figure 2

Kaplan–Meier survival curves for overall survival at the L3 level. The Kaplan–Meier survival curves for overall survival grouped by low and high (A) VFA, (B) IMFA, (C) SMA, (D) SFA, (E) SMD, and (F) SMI values at the L3 level. IMFA, intermuscular fat area; L3, lumbar 3 vertebra; SFA, subcutaneous fat area; SMA, skeletal muscle area; SMD, skeletal muscle density; SMI, skeletal muscle index; VFA, visceral fat area.

Figure 3

Kaplan–Meier survival curves for overall survival at the umbilical level. The Kaplan–Meier survival curves for overall survival grouped by low and high (A) VFA, (B) IMFA, (C) SMA, (D) SFA, (E) SMD, and (F) SMI values at the umbilical level. IMFA, intermuscular fat area; SFA, subcutaneous fat area; SMA, skeletal muscle area; SMD, skeletal muscle density; SMI, skeletal muscle index; VFA, visceral fat area.

Figure 4

Areas under the receiver operating characteristic curves for overall survival and disease‐free survival. Model 1: TNM stage. Model 2: TNM stage and VFA, IMFA, SMA, SFA, SMD and SMI. Model 3: TNM stage and independent prognostic factors (body composition and clinical indicators). (A–C) AUCs of the models for predicting overall survival. (D–F) The AUCs of models for predicting disease‐free survival. AUC, area under the curve; IMFA, intermuscular fat area; SFA, subcutaneous fat area; SMA, skeletal muscle area; SMD, skeletal muscle density; SMI, skeletal muscle index; TNM, tumour, node, metastasis; VFA, visceral fat area.