Optimal extent of lymph node dissection for T1 gastric cancer, with special reference to the distribution of micrometastasis, and accuracy of preoperative diagnosis for wall invasion

Background/aims Preoperative diagnosis for wall invasion and lymph node metastasis is sometimes difficult in T1 gastric cancer. Optimum dissection extent of lymph nodes for T1 gastric cancer was studied from the aspect of subclassification of wall invasion and lymph node metastasis including micrometastasis. Methodology 184 patients with cT1 or pT1 gastric cancer were studied. The grade of clinical wall invasion (cT) and clinical lymph node status (cN) were diagnosed by endoscopy and computed tomography or intraoperative findings. Lymph node metastasis (pN) was studied by hematoxylin and eosin staining and immunohistochemistry (IHC). Results In 79 cM tumors, 60 (75.9%) were diagnosed as pM. In 88 cSM tumors, 42 (47.7%) were diagnosed as pSM. In 94 pM gastric cancers, micrometastases were found in two patients (2.1%) and in N1 stations. Two (1.9%) of 70 pSM cancers had micrometastasis in No. 7, 8a and 12a stations. Lymph node metastasis (pN) correlated significantly with the depth of tumor invasion, lymphatic invasion and venous invasion. Regarding the pN2 stations, one (1.1%) of 94 pM tumors had lymph node metastasis in No.7 station, and 9 (12.9%) of 70 pSM tumors had nodal involvement in No.7, 8a, 11p, 12a and 14v stations. All eight pN+/cM tumors were diagnosed as nN0 and four (1.4%) of 23 pN+/cSM tumors were correctly diagnosed as pN+. In contrast, 8 (9.9%) of 81 cN0/cM tumors and 19 (24.1%) of 79 cN0/cSM tumors had histological lymph node metastasis (pN+). Conclusions Accuracy of the clinical diagnosis of lymph node metastasis is very low. Accordingly, prophylactic lymph node dissection is recommended even for cT1 and cN0 tumors. For cN0/cM cancer, D1+No.7 is recommended. D1+No.7, 8a, 9, 11p is recommended for cSM cancer, located in U or M region and additional dissection of No. 14v is recommended for cSM cancer located in L region.