The Prognostic Impact of Occult Lymph Node Metastasis in Node-negative Gastric Cancer: A Systematic Review and Meta-analysis

To conduct a meta-analysis to clarify whether occult lymph node metastasis (OLNM), which is identified by molecular detection techniques but is not detected by routine histological examination within regional lymph nodes, represents a prognostic factor for patients with node-negative gastric cancer. PubMed, Embase, and the Cochrane Library were searched from their inception to November 2012. The published studies that investigated the association between OLNM and the prognosis of patients with node-negative gastric cancer were included. We extracted hazard ratios (HRs) and associated standard errors from the identified studies and performed random-effects model meta-analyses on overall survival and disease-specific survival. Subgroup analyses were also conducted. A total of 14 eligible studies that included 1,478 patients were identified. Meta-analyses revealed that OLNM was associated with poor overall survival [HR 2.72; 95 % confidence interval (CI) 1.61-4.60], and disease-specific survival (HR 2.91; 95 % CI 1.25-6.79). Subgroup analyses suggested that OLNM was associated with poor survival in early gastric cancer (HR 3.57; 95 % CI 1.23-10.33). However, subgroup analyses of studies that exclusively enrolled patients with D2 lymph node dissection demonstrated that OLNM did not have an influence on the prognosis (HR 1.97; 95 % CI 0.82-4.70). OLNM correlates with poor prognosis for patients with node-negative gastric cancer, and D2 lymph node dissection could eliminate this correlation. For OLNM-positive patients with node-negative gastric cancer, D2 lymph node dissection is necessary.