Preoperative chemoradiotherapy changes the size criterion for predicting lateral lymph node metastasis in lower rectal cancer

Purpose The purpose of this study was to identify the size criteria of lateral lymph node metastasis in lower rectal cancer both in patients who underwent preoperative CRT and those who did not. Methods This study enrolled 150 patients who underwent resection for primary lower rectal adenocarcinoma with lateral lymph node dissection between 2013 and 2015. Patients were divided into two groups: the CRT group, treated with preoperative chemoradiotherapy before surgery, and the non-CRT group, treated with surgery alone. The short-axis diameter of each dissected lateral lymph node was measured. Receiveroperating characteristic curves were generated to reveal the optimal cutoff values for determining lateral lymph node metastasis in both groups. Results In the non-CRT group (n = 131), the ROC curve demonstrated that the optimal cutoff value for determining metastasis was 6.0 mm, with a sensitivity of 78.5% and specificity of 82.9%, and the AUC was 0.845. In comparison, in the CRT group (n = 19), the optimal cutoff value was 5.0 mm, with a sensitivity of 71.4% and specificity of 85.3% and an AUC of 0.836. Conclusion The cutoff size for determining lateral lymph node metastasis was smaller in the CRT group than in the non-CRT group.