Unexpected proximal tumor extension as a predictor of poor survival after distal gastrectomy for locally advanced gastric cancer.

[BACKGROUND] Unexpected horizontal tumor extension, quantified as the discrepancy between gross and pathological proximal margins (ΔPM), has been reported as a prognostic indicator in total and proximal gastrectomy, but its relevance in distal gastrectomy remains unclear.

[METHODS] Patients who underwent upfront distal gastrectomy with R0 resection for locally advanced gastric cancer at the Cancer Institute Hospital between 2015 and 2019 were retrospectively analyzed. ΔPM was calculated as the difference between gross and pathological proximal margin lengths. Optimal cutoff values were determined using ROC analyses. Overall (OS) and recurrence-free survivals (RFS) were assessed using Kaplan-Meier methods, and prognostic factors were evaluated through multivariate Cox regression and subgroup analyses.

[RESULTS] A total of 427 patients were included. ΔPM ≥7 mm was significantly associated with poorer 5-year OS (68.5% vs. 88.5%, p < 0.001) and RFS (61.8% vs. 84.9%, p < 0.001) compared with ΔPM <7 mm. In multivariate analysis, ΔPM ≥7 mm remained an independent predictor of OS (HR 2.15, 95% CI 1.27-3.64) and RFS (HR 2.01, 95% CI 1.23-3.29). Subgroup analyses showed a more pronounced adverse effect of ΔPM ≥7 mm in patients with cN-positive disease.

[CONCLUSIONS] A longer ΔPM is associated with substantially worse long-term outcomes after distal gastrectomy and serves as an independent indicator of aggressive tumor biology. This effect is particularly notable in cN-positive disease, suggesting potential value in guiding intraoperative management.