Pathological investigation of sentinel lymph nodes.

The sentinel lymph-node procedure enables selective targeting of the first draining lymph node, where the initial metastases will form. A negative sentinel node (SN) predicts the absence of tumour metastases in the other regional lymph nodes with high accuracy. This means that in the case of a negative SN, regional lymph-node dissection is no longer necessary. Besides saving costs, this will prevent many side-effects as a result of lymph-node dissection. The task of the pathologist is to screen SNs for metastases. To this end, several techniques are available such as standard histo- and cytopathological techniques, immunohistochemistry, flow cytometry, and molecular biological techniques. These methods are explained and their sensitivity for detecting SN metastases is discussed. Some of these techniques also appear to be useful for intra-operative evaluation of SNs. The standard protocol for detection of SN metastases consists of extensive histopathological investigation including step H&E stained sections and immunohistochemistry. Intra-operative frozen-section analysis of SNs has been shown to be reliable for breast-cancer axillary lymph nodes. In the intra-operative setting, imprint cytology can also be used but its additional value to frozen section analysis is not yet clear. Further studies are necessary to establish the role of sophisticated molecular biological techniques such as reverse transcription polymerase chain reaction (RT-PCR) in detecting SN metastases. The sensitivity of flow cytometry is too low for this purpose.