A sentinel lymph node biopsy is a procedure in which tissue is removed from the lymph nodes closest to an existing site of infection, cancer, or other disease. The test can help tell whether the condition has spread.

Lymph nodes are small glands found in groups throughout the body. These groups of nodes make up the lymph system, which helps the body to fight infections. If a biopsy of the sentinel node is positive for signs of infection or disease, there is a greater chance that the infection or disease has spread throughout the lymph system and bloodstream to other parts of the body.

For example, a woman with breast cancer who has a sentinel lymph node biopsy will usually have the tissue sample removed from the lymph nodes located under her arm. If the examination of the tissue does not show signs of cancer cells, it is not likely that the cancer has spread beyond the breast area.

Sentinel node biopsy is sometimes used instead of conventional lymph node dissection for staging cancer. It allows a doctor to obtain accurate information about the entire lymph system without making a person have more invasive surgery.