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MSI predicts favorable outcome in gastric carcinoma

Sentinel lymph nodes are the initial lymph nodes draining an area and are the most likely to contain early metastasis. Sentinel lymph node mapping has been used in melanoma and breast cancer to limit the extent of lymphadenectomy performed. More recently, this approach has been evaluated in colon cancer. Here, the goal is not to limit the extent of lymphadenectomy but rather to permit a focused detailed examination of these lymph nodes to determine the presence of metastatic disease. Although the presence of lymph node metastasis is recognized as an important prognostic factor in colon cancer and determines the need for systemic postoperative chemotherapy, rates of detection of lymph nodes in colon specimens is notoriously variable among institutions. Furthermore, conventional hematoxylin and eosin stains may not detect micrometastasis. By identifying the sentinel lymph node, a more focused examination, including multiple-level sectioning, immunohistochemical staining, and polymerase chain reaction assay, may improve the accuracy of the detection of metastatic disease. This is important because almost 30% of patients who are apparently node negative will have recurrence later. Wood et al. studied their first 100 patients with colorectal cancer on whom they performed sentinel lymph node mapping using peritumoral injection of isosulfan blue dye. A focused examination of multiple sections using cytokine immunohistochemistry was compared with hematoxylin and eosin staining on the sentinel nodes with routine staining of the remaining lymph nodes. Overall, sentinel nodes were identified in 97 of the 100 patients. These accurately reflected the status of the nodal basin in 92 of these 97 patients. There were five false-negative sentinel node exams. These all occurred early in the authors’ experience. Furthermore, eight patients had unexpected lymphatic drainage, which altered the lymphadenectomy performed. The focused examination upstaged 24% of patients who otherwise would have been negative by hematoxylin and eosin. The sentinel lymph nodes were the only positive nodes in 19 cases. Thus, sentinel lymph node mapping had a high degree of success and accuracy. This technique led to the identification of micrometastatic disease missed by conventional techniques in a significant portion of patients. This continues to be an active area of investigation in gastrointestinal oncology.