The removal of the sentinel lymph node (the first lymph node to which the cancer is likely to spread). A radioactive tracer and/or blue dye is injected near the tumor before surgery in a process called lymphatic mapping (or lymphoscintigraphy). The radioactive tracer or dye flows through the lymph channels in the skin to first draining lymph nodes in the region(s) around the melanoma. The injection of the radioactive tracer is performed in the Nuclear Medicine Department either the evening before surgery or several hours before surgery. A body scan is then performed to help the surgeon localize the sentinel lymph node before beginning the operation. This first lymph node(s) to receive the tracer is removed for biopsy. A pathologist then views the tissue under a microscope to look for cancer cells and often uses additional tissue stains (immunostains) to determine whether microscopic evidence of melanoma is evident in the regional lymph nodes. If cancer cells are not found, no further surgery is necessary.