Procedure in which a dye or radioactive substance is injected near the tumor. This material flows into the sentinel lymph nodes(s) (the first lymph node(s) that cancer is likely to spread to from the primary tumor). A surgeon then looks for the dye or uses a scanner to find the sentinel lymph node(s) and removes it or them in order to check for the presence of tumor cells.

A procedure in which only the sentinel node is removed to determine whether the cancer has spread to the lymph nodes.

Used in diagnosing skin cancer and breast cancer, a surgeon injects a radioactive substance into the area in question. Within an hour, lymph nodes are checked for radioactivity to find which one is the first to drain fluid. The lesion is then injected with a blue dye that will travel to the node where the cancer would first drain. When this first "sentinel" lymph node is located, it is removed and examined under a microscope. If cancer cells are found, the remaining the lymph nodes in the area are removed. If the sentinel node does not contain cancer cells, further lymph node surgery might not be needed.