Prognostic Value of Mesorectal Lymph Node Micrometastases in ypN0 Rectal Cancer After Chemoradiation

More than 25% of patients with node-negative colorectal cancer experience a recurrent disease even after curative surgery. This suggests the existence and oncologic influence of micrometastasis in regional lymph nodes or in distant organs. The objective of this study was to identify mesorectal lymph node micrometastases using an immunohistochemical analysis and to determine its prognostic value in node-negative rectal cancer after neoadjuvant chemoradiation. A total of 91 patients who received preoperative chemoradiation and radical resection for rectal cancer were included. Based on conventional hematoxylin and eosin staining, all patients had a node-negative disease. Mesorectal lymph nodes from resected specimens were re-evaluated to detect micrometastases by immunohistochemistry using anticytokeratin antibody AE1/AE3. The clinicopathologic data were collected from a prospectively maintained database of colorectal cancer patients and analyzed retrospectively. Micrometastases of mesorectal lymph nodes were detected in nine patients (9.9%). The three-year overall survival was similar regardless of micrometastasis (88.9% in the positive group versus 90.7% in the negative group, P = 0.681); however, the three-year disease-free survival was significantly poorer in the patients with micrometastases (40.0% versus 84.2%, P = 0.001). In the multivariate analysis, the advanced pT category (ypT3/T4 versus ypT0: hazard ratio [HR] 10.477, 95% confidence interval [CI] 1.102-99.594, P = 0.041) and micrometastases in mesorectal lymph nodes (HR 5.655, 95% CI 1.837-17.409, P = 0.003) were independent prognostic factors for disease-free survival. In node-negative rectal cancer after preoperative chemoradiation, immunohistochemically detected micrometastases of mesorectal lymph nodes were significantly correlated with poor disease-free survival.