A sentinel lymph node is the first lymph node that cancer is likely to spread to from a primary tumor. A sentinel lymph node biopsy identifies, removes, and examines this lymph node to determine if cancer cells are present. If cancer is found, it indicates the cancer may have spread to other lymph nodes or organs. Examining the sentinel lymph node helps determine the cancer stage and guides treatment planning. The procedure also reduces potential side effects of full lymph node surgery like lymphedema. Sentinel lymph node biopsies are used for cancers like breast cancer, melanoma, and others.