Clinicopathological characteristics of skipping lymph node metastases in patients with colorectal cancer.

BACKGROUND We have sometimes experienced cases of colorectal cancer with skipping lymph node metastasis in which distant nodes were positive but those closer to the tumor were negative. There have been few reports of this condition and its clinical characteristics have not been clarified. This study was conducted to clarify the status of skipping lymph node metastasis and its clinicopathological characteristics in colorectal cancer. METHODS We analyzed 452 patients with colorectal cancer and nodal metastases (270 with colon cancer and 182 with rectal cancer). All the resected nodes were examined using histological procedures with a microscope and were classified by their location according to the General Rules for Clinical and Pathological Studies on Cancer of the Colon, Rectum and Anus. We studied the status of skipping nodal status and the correlation between the nodal status and clinicopathological findings, including the disease-free survival, depth of tumor, histological type, staging and recurrence. RESULTS Twenty-eight (10.4%) of the colon cancer patients and 20 (11.0%) of the rectal cancer patients were found to have skipping nodal metastases. In rectal cancer patients with n2 (nodal metastases at the N2 site) in the direction of the main node, patients with skipping lymph node metastases had a significantly better prognosis than those without (p = 0.026). In all colon cancer patients and rectal cancer patients with lateral n3 (nodal metastases at the lateral N3 site), there were a tendency for those with skipping nodal metastases to have better disease-free survival rates (p = 0.1). Also, the mean number of positive nodes in skipping cases was significantly lower than that in non-skipping cases. In addition, skipping nodal metastases in rectal cancer suggested a possibility of bypass flow which was not generally recognized. CONCLUSION These findings in colorectal cancer suggest the presence of previously unknown lymphatic tracts and that the cancers concerned have a better prognosis than those without skipping nodal metastases.