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The information on this page was reviewed and approved by
Maurie Markman, MD, President, Medicine & Science at CTCA.

This page was updated on April 5, 2021.

Sentinel lymph node biopsy

Sentinel lymph node biopsy is used to diagnose and stage cancer by helping to determine whether the cancer has spread (metastasized). During a sentinel lymph node biopsy (SLNB), a radioactive substance and/or a blue dye is injected near the tumor site. Cancer spreads to the lymphatic system in a predictable pattern, which can be observed through lymphatic mapping. The first lymph nodes to absorb the radioactivity from the dye are identified as sentinel lymph nodes (SLN), because they are the first lymph nodes where lymphatic vessels drain. The tumor cells are most likely to spread from a primary tumor to nodal metastases in those locations. More than one lymph node may be considered sentinel, or vulnerable to sentinel node metastasis.

The surgeon removes the sentinel lymph nodes for examination by a pathologist, who tests the tissue for the presence of cancer cells. The biopsy procedure is sometimes referred to as sentinel lymph node dissection because it involves removing just a few lymph nodes for testing. If the sentinel nodes show no signs of cancer, the cancer is less likely to have spread, and the oncologist may recommend no further testing of nearby lymph nodes. This node-negative determination helps inform oncologists in recommending an appropriate treatment plan, while avoiding the unnecessary removal of healthy lymph nodes.

For a patient with positive sentinel lymph node results, axillary lymph node dissection (ALND) may be needed to remove more lymph nodes, depending on the lymph node metastasis and number of lymph nodes involved. In some circumstances, a sentinel lymph node biopsy may be performed at the same time, before or after the primary tumor is removed.

A sentinel lymph node biopsy is often recommended for early-stage breast cancer patients to determine whether cancer has spread to the axillary lymph nodes, located in the armpit. Sparing healthy lymph nodes in the axilla area may help prevent a condition known as lymphedema, which leads to excess fluid buildup and swelling in the tissue, most often in the extremities, such as the arms and legs. A sentinel lymph node biopsy may also be performed at the same time as another surgical procedure, such as a lumpectomy or mastectomy.

A sentinel lymph node biopsy may be an option for melanoma patients whose cancer has a high risk of spreading to the lymph nodes. Sentinel lymph node biopsy is also typically recommended for some patients to determine whether their gynecologic cancer has spread to the lymphatic system. The biopsy results may help the oncology team decide whether to remove all the regional lymph nodes in the pelvic area, which may reduce the risk of complications common to surgeries for gynecologic cancer.