This is a procedure used to help identify the sentinel lymph node(s), which is the first lymph node to where cancer cells are likely to spread from the primary tumor.
In patients with Breast Cancer, the procedure involves injecting a radioactive isotope (technetium sulfur colloid) into the breast, generally around the central aspect of the breast. The material moves through the lymphatic channels and accumulates in one or several lymph nodes. During surgery, a handheld gamma ray counter scans the area of the underarm to locate the sentinel node(s).
In patients with Melanoma, the injections are performed around the area where the original lesion was located on the body. The handheld gamma ray counter scans the body during surgery to locate the sentinel nodes(s) in these cases as well.