Background: Currently, gastric cancer staging systems do not consider the anatomic extent of metastatic lymph nodes (mLNs) as a prognostic factor. We therefore investigated the prognostic impact of the anatomic extent of mLNs on gastric cancer. Methods: The prognoses of 4,043 gastric cancer patients who underwent curative resection were analyzed. Patients with mLNs in lymph node (LN) stations 1-6 (n = 1,980) comprised the perigastric LN-positive (PLN) group, and patients with mLNs in LN stations 7-12 and 14 (n = 2,063) were assigned to the extraperigastric LN-positive (ELN) group. Overall survival was estimated using the Kaplan-Meier method, and hazard ratios (HRs) were calculated by the Cox proportional hazard model. Results: The ELN group exhibited worse survival than the PLN group (p < 0.001), although there were differences in their clinicopathological features. When patients were stratified according to tumor-node-metastasis stage, the ELN groups had unfavorable prognoses compared with the PLN groups (p < 0.05). There were significant differences in long-term survival when the nodal stage of the current staging systems were subdivided according to anatomic nodal extent (p < 0.05), although there was a strong association between the probability of having extraperigastric mLNs and N classification. In multivariate analysis using age, gender, tumor size, tumor location, histology, T classification, and the extent of mLNs as covariates, presence of extraperigastric mLNs was an independent prognostic factor (HR 1.89, 95 % CI 1.73-2.07), along with age, tumor size, tumor location, and T classification. Conclusions: The anatomic extent of mLNs significantly affects patient prognosis. Including the anatomic extent of mLNs in the current staging system may predict gastric cancer prognosis more accurately in patients with the same stage of cancer.
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