What is a Sentinel Lymph Node Biopsy?

A biopsy is when a sample of tissue is removed and studied to examine the cells it contains and, in a sentinel lymph node biopsy, the tissue which is taken involves the first few lymph nodes traveled to by cancer cells when they begin to spread. Lymph nodes are small rounded structures that filter the fluid that circulates through the lymphatic system, removing foreign, potentially harmful matter such as bacteria. In some types of cancer the malignant, or cancerous, cells typically spread through the lymphatic system and can be found in lymph node tissue when it is examined under a microscope. Since the sentinel lymph nodes are the first ones the cancer cells would normally reach, if they are found to be clear of cancer it makes it more likely that the cancer has not yet spread, or metastasized.

Sentinel lymph node biopsy procedures are used in the management of a number of cancers which spread through the lymphatic system. Some examples include melanoma, and other skin cancers, and breast cancer. In the past, when surgery was used to assess whether such cancers had spread as far as nearby lymph nodes, it was usual to remove all of the nearest group, which could contain up to 30 nodes, as it was uncertain which ones might contain the cancer. This has the disadvantage that a larger area of the body is surgically removed compared with a sentinel lymph node biopsy, which typically removes up to three nodes. Problems such as pain, restricted movement, swelling due to accumulation of lymph fluid, and nerve damage are more common with the more extensive procedure.

A sentinel lymph node biopsy begins with the surgeon injecting a tiny quantity of mildly radioactive tracker material into the area near the tumor. Sometimes a blue dye is also injected to act as a visual marker. The radioactive substance and the dye drain from the tumor area into the lymphatic system, using the same route that spreading cancer cells would take. Later, in the operating theater, by using a handheld Geiger counter which detects radioactivity, and moving it gradually from the tumor towards nearby lymph nodes, the surgeon can locate the first nodes reached by the tracker material. These can be removed and examined for cancer cells, with the blue dye being an additional marker to help ensure the correct nodes have been selected.

The advantages of carrying out a sentinel lymph node biopsy include the fact that it is a less traumatic process for the patient, with fewer likely complications and a quicker recovery. If the sentinel nodes are found to be free from cancer cells then there is no need to remove the remaining lymph nodes, so the patient is spared from a larger operation. Where cancer is found to have spread to the sentinel nodes then the rest of the group of lymph nodes will be removed as well.