The study of regional lymph nodes is important to establish the staging of melanoma and therefore it includes the possibility of a distant spread of melanoma. Sentinel lymph node is the first lymph node which drains a cutaneous region in a lymphatic basin. It seems to be the most probable site of melanoma metastasis. The technique of sentinel lymph node was proposed by Morton in 1990 and adapted to melanoma in 1992, it is micro-invasive technique with high prognostic value that is performed with the selective removal of lymph nodes that drain the area where is located the melanoma. The removal of lymph node predicts that melanoma has metastasized the lymph node basin. If the examination is positive, the patient undergoes a radical lymphadenectomy, if the test result is negative it means that regional lymph nodes are free of metastasis and then the patient is strictly monitored.
The study of the sentinel node is performed in stages T2, T3, T4 and T1b (ulceration) and extended in cases with high mitotic rate, in melanoma with regression, if there is angiolymphatic invasion and young age. The examination is executed after the instrumental tests have ruled out the presence of distant metastases, injecting a blue colored dye (patent blue-V or biosolfan blue) or a radioactive tracer (technetium 99m: Nanocoll or lymphoscint: colloidal particles from 50 to 100 nm) around the site of a primary melanoma. The area is scanned by a gamma counter. After the injection of dye, waiting half hour for the dye to travel through the lymph vessels to the node, the surgeon then reexcises the site of the melanoma. If there is a hot or blue node, it is removed for a pathology examination. In 15% of cases the sentinel node may be different from the one that has greater uptake. Lymph node is divided into two halves, frozen at -25°C; then several 6-microns sections (from 6 to 8) are stained stained with hematoxylin and eosin and then is performed immunohistochemistry with S100 (It marks almost 100% of micrometastases, but also dendritic cells or Langerhans cells and neural origin) and HMB45 (more specific for melanoma but with a reduced sensitivity compared to S100) and examined at microscope. Malignant cells are found frequently in the subcapsular sinus, sometimes in cortical or medullary sinuses of the lymph node. If the sentinel node reveals melanoma cells a complete node dissection is executed to stop the disease from spreading furtherIf the test is negative no further surgery is necessary. A negative sentinel node does not exclude the presence of metastasis because malignant cells may pass through other lymphatics. Some factors that limit the meaning of this, the presence of a window period in which the malignant cells have not yet arrived at the node and also the presence of melanoma in critical areas such as the trunk and cephalic area. In the cephalic area is recommended to search the node by SPET / CT because it allows a perfect identification of the location of the sentinel node, in this area dye is not used because it can leave permanent tattoos on face.In recent years, techniques have been added to the histological research of micrometastases by polymerase chain reaction of the reverse transcriptase, of ‘tyrosine messenger RNA (It appears as the most sensitive technique in the sentinel node in the search of occult melanoma cells). This method is very sensitive, but very expensive and not available in all centers. Studies show that the technique of sentinel lymph node can increase the survival rate of patients with melanoma. False negatives are about 5% and local complications in the order of 8%.
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sentinel lymph node biopsy