Should lymph node micrometastasis be considered in node staging for gastric cancer?: the significance of lymph node micrometastasis in gastric cancer.

BACKGROUND: In TNM staging system, lymph node staging is based on the number of metastatic lymph nodes in gastric cancer and micrometastasis is not considered. Several reports proposed the importance of lymph node micrometastasis as the causative factor for recurrence and poor survival, but it remains controversial among researchers.
METHODS: A total of 482 gastric cancer patients who underwent curative resection from 2004 to 2010 at Korea University Medical Center Ansan Hospital, South Korea were prospectively enrolled. For detecting lymph node micrometastasis, immunohistochemical staining with anti-cytokeratin antibody (CAM 5.2) was performed on negative lymph nodes by hematoxylin-eosin (H-E) staining. Survival differences were compared between conventional node staging and new node staging that took micrometastasis into consideration. Also, the prognostic value of lymph node micrometastasis was investigated in multivariate analysis.
RESULTS: A total of 156 patients (32.4%) showed lymph node micrometastasis. Overall, the micrometastatic group had more advanced tumor and lymph node stage, lymphovascular cancer cell invasion, a higher rate of recurrence, and poor survival. Furthermore, when the cumulative numbers of macro- and micrometastatic lymph nodes were calculated together, the discriminative power of survival difference between each node stage became more stratified. Also, multivariate analysis using Cox's proportional hazards model demonstrated perineural invasion, pathologic T stage, dissected lymph nodes, macro- and micrometastatic lymph nodes are independent prognostic factors.
CONCLUSIONS: Lymph node micrometastasis was clinically significant as a risk factor for recurrent gastric cancer. Lymph node micrometastasis should be considered when estimating TNM stage for determining prognosis and the best treatment strategy.