Prediction of metastasis to mesorectal, internal iliac and obturator lymph nodes according to size criteria in patients with locally advanced lower rectal cancer

Objective: This study was performed to clarify whether size criteria could be applied to the prediction of metastasis to the mesorectal, internal iliac and obturator lymph nodes in patients with lower rectal cancer. Methods: A total of 915 lymph nodes (416 mesorectal, 199 internal iliac and 300 obturator) from 53 patients with lower rectal cancer who underwent a curative resection were examined; 83 lymph nodes were positive. The sizes of the lymph nodes immediately after removal and those of paraffinembedded sections were compared for 175 lymph nodes. Then, size criteria for discriminating the status of metastasis were evaluated in 915 paraffin-embedded lymph nodes. Results: Regardless of the metastatic status and the site of the lymph nodes, a positive relationship was observed between the sizes of the lymph nodes immediatelyafter removal and those of paraffinembedded sections (P < 0.01). The area under the curve generated by a receiver-operating characteristics curve showed no significant differences between the short-axis diameter and the long-axis diameter, regardless of the lymph node location. Specifically, the optimal cutoff value of the short-axis diameter for discriminating the status of metastasis in mesorectal, internal iliac and obturator lymph nodes extrapolated to the living body was set at 6.2, 5.0 and 4.8 mm, with accuracies of 72.4, 63.8 and 59.3% and with positive predictive values of 29.9, 16.3 and 7.1%, respectively. Conclusions: Size criteria were applicable for discriminating the metastatic status of lymph nodes from threedifferent locations, althoughthe positive predictive valuesofthe size criteriafor the internal iliac and obturator lymph nodes were lower than that for the mesorectal lymph nodes.