The sentinel node in colorectal carcinoma. Mapping technique, pathologic assessment, and clinical relevance

One of the most important prognostic factors in colorectal cancer is the presence or absence of regional lymph node metastases. In many instances, micrometastatic disease may not be found on routine pathologic analysis using hematoxylin and eosin staining, but may be discovered only with immunohistochemical methods or polymerase chain reaction assay. Lymphoscintigraphy with biopsy of the sentinel nodes, defined as the first nodal basin in the drainage pathway of a tumor, was developed to provide accurate staging without the morbidity associated with the classic lymph node dissections performed for melanoma or breast cancer. This concept has recently been applied to colorectal cancers, but the method used is unique because oncologic principles of resection are still adhered to for the primary tumor along with en bloc resection of the locoregional mesenteric nodes, some of which are sentinel nodes. Sentinel nodes are ideal for sensitive pathologic techniques of detecting micrometastatic disease, as they often reflect the status of the entire locoregional nodal basin. Gross metastatic nodes reveal significant prognostic information and guide the use of adjuvant therapy in affected patients. However, the detection of micrometastatic disease in sentinel nodes by sensitive pathologic methods has not been proven to result in poor prognosis or benefit from adjuvant therapy for colorectal cancer.