Improving prediction of lateral node spread in low rectal cancers-multivariate analysis of clinicopathological factors in 1,046 cases

This study aims to search for independent predictors of lateral node metastasis in low rectal cancers. We analyzed 1,046 patients who underwent curative resection for lower rectal cancer in our prospectively collected database. All lymph nodes were dissected from the fresh specimen, and their locations were documented prospectively according to the classification by the Japanese Society of Cancer of the Colon and Rectum. More than 35% of the patients had demonstrated upward nodal metastasis in the direction of the inferior mesenteric vessels, while 11% demonstrated lateral node metastasis, which was present in 17.3% of patients with T3 and T4 lesions. Multivariate analysis revealed five factors to be statistically significant independent predictors of lateral node metastasis: female sex, tumors that were not well differentiated, pathological T3 and above, positive microscopic lymphatic invasion, and positive mesorectal nodes. Using the variables sex, differentiation, T stage, and mesorectal nodes as risk factors, because these could be elucidated preoperatively, the presence of lateral node metastasis was then analyzed according to the number of positive risk factors. When there were fewer than three positive factors, the risk of lateral nodal spread was low (4.5%). When three or more risk factors were positive, the odds of lateral node metastasis were more than 7.5 times higher (p < 0.001). The findings of this study provide a scoring system that can be used to guide the clinician to the presence of lateral node metastasis in low rectal cancers.