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Melanoma is a type of cancer that starts in color-producing cells of the skin called melanocytes. Often, but not always, melanoma develops from an existing mole. Melanoma can grow deep into the inner layers of skin and spread to the lymph nodes (tiny, bean-shaped organs that help fight infection) and other parts of the body. Treatment for melanoma is determined by the thickness (how deep the tumor has grown into the layers of the skin) of the primary tumor and whether it has spread. This is also called the stage of the cancer. Whether melanoma has spread to the lymph nodes is one of the most important factors in determining a patient’s prognosis (chance of recovery).
A sentinel lymph node biopsy (also called sentinel node biopsy or SNB) is a procedure that helps the doctor find out whether the cancer has spread to the lymph nodes. When cancer spreads from the place it started to the lymph nodes, it travels through the lymphatic system. A sentinel lymph node is the first node into which the lymphatic system drains. Because melanoma can start anywhere on the skin, the location of the sentinel lymph nodes will be different depending on where the cancer started. To find the sentinel lymph node, a harmless radioactive substance is injected as close as possible to where the melanoma started. The substance is followed to the sentinel lymph node. Then, the doctor removes one or a few of these lymph nodes to check for melanoma cells, leaving behind most of the other lymph nodes in that area.
If the biopsy results show that the cancer has not spread to the sentinel lymph node, then no additional lymph node surgery is needed. However, if melanoma is found in the sentinel lymph nodes, a lymph node dissection is usually recommended. A lymph node dissection is the surgical removal of the remaining lymph nodes in that area. The risks of a lymph node dissection vary depending on the number of lymph nodes removed during the procedure.