Background: The relationship between postoperative changes in muscle mass and the prognosis of malignancies remains controversial. We aimed to determine whether a decrease in skeletal muscle mass after surgical resection can predict long-term outcomes in patients with adenocarcinoma of upper stomach (AUS) and esophagogastric junction (AEGJ). Methods: We reviewed 146 patients who underwent curative surgery for AUS and AEGJ. We assessed the skeletal muscle index pre- and post-surgery and 6 months postoperatively. The rate of decrease in skeletal muscle index (SMI) was calculated and its relationship with clinicopathological factors and prognosis was analyzed. Results: Among the 146 patients studied, 115 underwent re-assessment of SMI 6 months postoperatively. The mean decrease in SMI was more prominent in patients with recurrence than in those without recurrence (19.0 ± 2.3 vs. 7.4 ± 0.9%, respectively, P < 0.0001). AUS and AEGJ patients with a >19% decrease in SMI showed significantly lower 5-year overall survival and recurrence-free rates than those with a <19% decrease in SMI (recurrence-free survival: 33.4 vs. 89.2%, respectively, P < 0.0001; overall survival: 40.6 vs. 90.0%, respectively, P < 0.0001). Multivariate analyses indicated that a ≥19% decrease in SMI could predict poor overall survival independently in patients with AUS and AEGJ (P = 0.0070). Conclusions: A ≥19% postoperative decrease in SMI was substantially associated with poor survival in patients with AUS and AEGJ.
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