PURPOSE:Lymph node metastasis in colorectal carcinoma is an important prognostic factor, yet the prognostic relevance of occult tumor cells in lymph nodes has not elucidated. This study was performed to investigate the correlation between isolated tumor cells in lymph nodes and malignancy potential in patients with Dukes B colorectal carcinoma and, thus, to determine whether presence of isolated tumor cells in lymph nodes has a prognostic significance.METHODS:To evaluate the incidence of isolated tumor cells in lymph nodes in patients with Dukes B colorectal carcinoma, 1,808 lymph nodes taken from 93 patients (19.4 per case) were assessed by immunohistochemical technique using a monoclonal antihuman cytokeratin (MNF 116). Clinicopathologic parameters and prognosis were compared between patients with and without isolated tumor cells.RESULTS:Isolated tumor cells were identified in 54 lymph nodes from 29 patients (31.2 percent) by the immunostaining. No correlations were observed between the incidence of positive isolated tumor cells and various clinicopathologic parameters, including preoperative carcinoembryonic level, tumor site and size, histologic differentiation, pT stage, vascular invasion and lymphatic invasion, and perineural invasion. There was no difference in five‐year survival estimated by Kaplan‐Meier life‐table method between positive and negative groups for isolated tumor cells (82.8 and 85.9 percent, respectively). Multivariate analyses showed that sex (P= 0.0236), serum carcinoembryonic level (≥ 5 ng/ml,P= 0.0002), and lymphatic vessel invasion (P= 0.0002) were significant factors in the survival time.CONCLUSION:Immunohistochemical staining with an anticytokeratin antibody is useful in identifying isolated tumor cells in lymph nodes missed in routine hematoxylin‐eosin staining, but clinically it seems to be of little prognostic value in patients with Dukes B colorectal carcinoma. Thus, this immunostaining technique does not offer a significant benefit of different strategies for additional therapy or follow‐up during conventional pathologic staging using hematoxylin‐eosin staining.