Quantitative RT-PCR Detection of Tumor Cells in Sentinel Lymph Nodes Isolated From Colon Cancer Patients with an Ex Vivo Approach

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To investigate quantitative RT-PCR-based detection of tumor cells in lymph nodes (LNs) isolated from colon cancer patients by ex vivo sentinel lymph node (SLN) mapping. Although lymph node status is among the strongest prognostic factors in colon cancer patients, 20% to 30% of node negative patients experience disease recurrence. These patients may have LN metastases that are not detected by routine examination. Ex vivo SLN mapping was applied to 131 prospectively recruited patients undergoing curative surgery for primary colon cancer. The SLNs were analyzed for the presence of tumor cells by routine histology and real-time RT-PCR quantitation of cytokeratin 20 (CK20) and mucin 2(MUC2) mRNA. SLNs were identified in 125 (95%) of the 131 patients included.Routine histologic analysis of SLNs and other regional lymph nodes revealed LN metastases in 42 patients (N+), of which 29 (69%) had metastases detected in 1 or more SLNs (sensitivity, 69%; false negative rate, 31%).When analyzing the SLNs by quantitative RT-PCR, the sensitivity, compared with routine LN examination, was 37/42 (88%) for both the CK20 and the MUC2 mRNA markers. In addition, 46% and 27% of the patients' node negative by routine LN examination (N0) were positive for the CK20 and MUC2 mRNA markers, respectively, possibly reflecting the presence of occult tumor cells in their SLNs. Quantitative RT-PCR analysis of SLNs identified N+ patients with high sensitivity and revealed a subgroup of N0 patients with potential occult LN disease.