Lymph nodes from patients with colorectal cancer were immunohistochemically stained for cytokeratin to investigate the relationship between the presence of occult neoplastic cells (ONCs) and recurrence/metastasis. A total of 80 patients with stage III/Dukes' C colorectal cancer were divided into 16 patients who developed recurrence/metastasis (recurrence group) and 64 patients without recurrence (non-recurrence group). ONCs were compared between the two groups with respect to i) single cells (≥3 floating ONCs), ii) clusters of cells (1 or more floating aggregates of 2-20 ONCs) and iii) single cells + clusters. When single cells were detected, the sensitivity for recurrence was 87.5% (14/16, p=0.002), the positive predictive value (PPV) was 32.6% (14/43), the specificity was 54.7% (35/64) and the negative predictive value (NPV) was 94.6% (35/37). For clusters, the sensitivity was 87.5% (14/16, p<0.001), PPV was 41.2% (14/34), specificity was 68.8% (44/64) and NPV 95.7% (44/46). With single cells + clusters, the values were 87.5% (14/16, p<0.001), 48.3% (14/29), 76.6% (49/64) and 96.1% (49/51), respectively. These results suggest that the detection of single cells + clusters is a sensitive indicator of a high risk of recurrence/ metastasis, while ONCs are useful for identifying the low-risk group of patients with stage III colorectal cancer.

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