Use of Sentinel Node Mapping for Cancer of the Colon: ‘To Map or Not to Map’

Sentinel lymph node (SLN) mapping has become a cornerstone of oncologic surgery because it is a proven method for identifying nodal disease in melanoma and breast cancer. In addition, it can ameliorate the surgical morbidity secondary to lymphadenectomy. However, experience with SLN mapping for carcinoma of the colon and other visceral malignancies is limited. This study represents an update to our initial pilot experience with SLN mapping for carcinoma of the colon. Consenting patients over the age of 18 diagnosed with adenocarcinoma of the colon were included in this study. At the time of operation, 1 to 2 mL of isosulfan blue was injected with a 25-gauge needle into the subserosa at 4 sites around the edge of the palpable tumor. The SLN was identified visually and excised followed by a standard lymphadenectomy and surgical resection. SLNs were evaluated by standard hematoxylin and eosin (H&E) evaluation as well as immunohistochemical (IHC) techniques for carcinoembryonic antigen and cytokeratin if the H&E was negative. Sixty-nine patients underwent SLN mapping. A SLN was identified in 93 per cent (64 of 69) of patients. Nodal metastases were identified in 38 per cent (26 of 69) of patients overall. In 5 patients, the only positive node identified was the SLN, 2 of which were positive by IHC criteria alone. Therefore, 3 per cent (2 of 69) of patients were upstaged by SLN mapping. This technique was 100 per cent specific while being 46 per cent sensitive. Fourteen patients had false-negative SLNs. Metastasis to regional lymph nodes remains the key prognostic factor for colon cancer. SLN mapping is feasible for colon cancer and can identify a subset of patients who could benefit from adjuvant chemotherapy. Although SLN mapping did not alter the surgical management of colon cancer, it does make possible a more focused and cost-effective pathologic evaluation of nodal disease. We do not suggest routine utilization of SLN mapping for colon cancer, but we believe that the data supports proceeding with a national trial.