A proposal for grading the risk of lymph node metastasis after endoscopic resection of T1 colorectal cancer.

Purpose: At present, for patients with early colorectal cancer as long as having any one risk factor of lymph node metastasis (LNM) after endoscopic resection (ER), additional surgery will be considered, regardless of the degree of LNM risk; however, most patients are free of LNM. This study aimed to further grade these patients according to LNM risk.

Methods: We assessed 271 patients with T1 colorectal cancers treated initially with ER to analyze the correlation between LNM-associated risk factors and LNM rate. Differences in this rate between groups were estimated using the χ test or Fisher's exact test.

Results: Poorly differentiated adenocarcinoma (Por) (3.4% vs. 40%, p < 0.001) and lymphovascular infiltration (LV) (1.6% vs. 29.0%, p < 0.001) were the only parameters correlated with LNM. When we divided the cases into LV-negative (LV(-)) and LV-positive (LV(+)) groups, we found a significantly higher LNM rate in the LV(+) group (29.0% vs. 1.6%, p < 0.001). Additionally, the rate of LNM in those positive for each parameter did not differ from the control rate in the same group, except in the Por subgroup. When the cases were divided into four groups based on the presence of LV infiltration and Por, the LNM rate in each group was 2/233 cases (0.8%) in the LV(-)Por(-) group, 2/7 cases (28.5%) in the LV(-)Por(+) group, 7/28 cases (25.0%) in the LV(+)Por(-) group, and 2/3 cases (66.6%) in the LV(+)Por(+) group.

Conclusions: Based on LV and histological differentiation, patients were classified into three LNM risk grades: low (LNM, 0.8%), moderate (LNM, 25.0-28.5%), and high (LNM, 66.6%).