Evaluation of endoscopic mucosal resection and nodal micrometastasis in pN0 submucosal gastric cancer

Endoscopic mucosal resection (EMR) is a minimally invasive, standard treatment for intramucosal (early) gastric cancers, but is not standard for submucosal gastric cancers based on existing criteria. We evaluated the possibility of extending EMR as a therapy for submucosal gastric cancers by analyzing nodal micrometastasis through immunohistochemical staining in patients with apparent node-negative submucosal gastric cancer, the patients for whom EMR might be appropriate. We used anti-cytokeratin (AE1/AE3) antibody to immunohistochemically detect nodal micrometastasis that was not identified by routine pathological examination in 162 patients (total, 2048 lymph nodes) with apparent node-negative submucosal gastric cancer. The relationship between the incidence of nodal micrometastasis and clinicopathological factors was analyzed. Micrometastasis was detected in 45 of 2048 nodes (2.2%), representing 31 of 162 patients (19%). A significantly high incidence of nodal micrometastasis was found with submucosal cancers of large size (>2 cm), as well as with tumors that showed lymphatic or venous invasion and deeper submucosal invasion (p<0.0001). Nodal micrometastasis was also recognized in 2 cases of histologically well-differentiated tumors with focal submucosal invasion without venous or lymphatic invasion. Of the 162 patients, only 2 died of recurrent disease regardless of nodal involvement. Based on the present results, risk factors for nodal micrometastasis are tumor size, presence of lymphatic-vascular invasion, and depth of tumor, which are nearly the same as those established in previous pathological studies that used hematoxylin and eosin staining. We conclude that EMR is not recommended for patients with submucosal gastric cancer.