Combination probe and dye-directed lymphatic mapping detects micrometastases in early colorectal cancer

Nodal metastasis is the single most important prognostic factor in early colorectal cancer (CRC). Lymphatic mapping can identify sentinel nodes for focused histopathologic examination and thereby improve the nodal staging of CRC; however, the optimal technique for identifying sentinel nodes in CRC is unclear. We hypothesized that a combination of radiotracer and blue dye would more accurately identify tumor-positive sentinel nodes than blue dye alone. Lymphatic mapping was performed in 48 consecutive patients undergoing resection for CRC and in two original patients who underwent sentinel node mapping in 1996. Prior to resection, 1% vital blue dye and radiotracer were injected around the tumor in the subserosal layer. Nodes were designated as sentinel by blue coloration and/or radioactivity. Lymphatic mapping identified at least one sentinel node in 49 patients. Focused examination of multiple sentinel node sections by means of hematoxylin and eosin and immunohistochemical analysis showed that sentinel nodes accurately predicted the status of the nodal basin in 93.8% (46 of 49) of patients. Of the 19 patients with nodal metastases, 11 had macrometastases (>.2 mm), three had micrometastases (between 2 mm and 0.2 mm), and five had isolated tumor cells or clusters (<.2 mm) identified by immunohistochemical analysis only. Patients had significantly fewer blue/radioactive ("hot") nodes than blue-only nodes (1.38 vs. 2.48 per patient; P = 0.0001). It is important to note that nodal metastases were more common in blue/hot nodes than in blue-only nodes (27.3% [19 of 68] vs. 8.8% [11 of 124]; P = 0.005). Dual-agent lymphatic mapping more accurately identifies sentinel node metastases than blue dye alone. In addition, this technique allows a more focused histopathologic examination of these nodes, in conjunction with the revised American Joint Committee on Cancer guidelines, and thereby offers the potential for significant upstaging of CRC.