Abstract Aim Sarcopenia is associated with poor postoperative outcomes in various cancers; however, limited evidence is available for rectal cancer. Therefore, the present study examined the effects of skeletal muscle mass on the short‐ and long‐term outcomes of rectal cancer. Materials and Methods A total of 787 Stage I–IV rectal cancer patients who underwent curative resection between 2003 and 2021 at The University of Tokyo Hospital were included. We conducted a propensity score‐matched analysis to mitigate confounding bias. The third lumber psoas muscle mass was measured to define sarcopenia. Results Among 787 patients, 350 (44.5%) were classified as having sarcopenia. After matching, 532 patients were analyzed. Patient characteristics in the sarcopenia and nonsarcopenia groups were similar; however, the body mass index differed. The sarcopenia group had significantly higher rates of postoperative complications of all grades (33.1% vs 24.8%; p = 0.035), of grade ≥2 (29.3% vs 21.8%; p = 0.047), and anastomotic leakage (1.9% vs 0%; p = 0.0082) than the nonsarcopenia group. The 5‐y overall survival rate was significantly lower in the sarcopenia group than in the nonsarcopenia group (85.3% vs 91.8%, p = 0.019). Disease‐free survival was similar between the groups ( p = 0.40). In the total cohort analysis, sarcopenia was an independent risk factor for total postoperative complications (odds ratio 1.41, p = 0.042). Conclusion Preoperative sarcopenia is associated with more total postoperative complications, more anastomotic leakage, and worse survival in rectal cancer patients.
