Background: Sarcopenia affects the prognosis of patients with cancer. The goal of the study was to investigate the relationship of skeletal muscle loss with prognosis after chemotherapy for recurrence after radical surgery for colorectal cancer.

Methods: The subjects were 50 patients who underwent chemotherapy due to recurrence after radical surgery for colorectal cancer from April 2010 to March 2021 and received best supportive care after the end of chemotherapy. Associations of skeletal muscle loss and clinicopathological factors with the post-chemotherapy prognosis were investigated.

Results: Univariate analysis showed significant relationships of age, lower skeletal muscle change ratio, decreased PNI, mGPS 2, and reduced oral intake with poorer prognosis. In multivariate analysis, a lower skeletal muscle change ratio was an independent poor prognostic factor (hazard ratio 0.94, p = 0.017). In Kaplan-Meier analysis, the 90-day survival rates after chemotherapy were 0.26 [95% confidence interval (CI): 0.10–0.47] and 0.87 (95% CI: 0.68–0.95) for skeletal muscle change ratios of <90.5% and ≥90.5%, respectively. A log rank test showed a significant relationship between skeletal muscle change ratio <90.5% and a poor prognosis (p < 0.001).

Conclusion: The skeletal muscle change ratio is associated with prognosis after chemotherapy for recurrent colorectal cancer and may be a useful indicator for 90-day survival.