Sentinel Lymph Node Biopsy Health Article

Definition

Sentinel lymph node biopsy (SLNB) is a minimally invasive procedure in which a lymph node near the site of a cancerous tumor is first identified as a sentinel node and then removed for microscopic analysis. SLNB was developed by researchers in several different cancer centers following the discovery that the human lymphatic system can be mapped with radioactive dyes, and that the lymph node(s) closest to a tumor serve to filter and trap cancer cells. These nodes are known as sentinel nodes because they act like sentries to warn doctors that a patient's cancer is spreading.

The first descriptions of sentinel nodes come from studies of penile and testicular cancers done in the 1970s. A technique that uses blue dye to map the lymphatic system was developed in the 1980s and applied to the treatment of melanoma in 1989. The extension of sentinel lymph node biopsy to the treatment of breast cancer began at the John Wayne Cancer Institute in Santa Monica, California, in 1991. As of 2003, SLNB is used in the diagnosis and treatment of many other cancers, including cancers of the head and neck, anus, bladder, lung, and male breast.

Purpose

Sentinel lymph node biopsy has several purposes:

• Improving the accuracy of cancer staging. Cancer staging is a system that classifies malignant tumors according to the extent of their spread in the body. It is used to guide decisions about treatment.
• Catching the spread of cancer to nearby lymph nodes as early as possible.
• Defining homogeneous patient populations for clinical trials of new cancer treatments.

Description

A sentinel lymph node biopsy is done in two stages. In the first part of the procedure, which takes one to two hours, the patient goes to the nuclear medicine department of the hospital for an injection of a radioactive tracer known as technetium 99. A doctor who specializes in nuclear medicine first numbs the area around the tumor with a local anesthetic and then injects the radioactive technetium. He or she usually injects a blue dye as well. The doctor will then use a gamma camera to take pictures of the lymph nodes before surgery. This type of imaging study is called lymphoscintigraphy.

After the lymphoscintigraphy, the patient must wait several hours for the dye and the radioactive material to travel from the tissues around the tumor to the sentinel lymph node. He or she is then taken to the operating room and put under general anesthesia. Next, the surgeon injects more blue dye into the area around the tumor. The surgeon then uses a hand-held probe connected to a gamma ray counter to scan the area for the radioactive technetium. The sentinel lymph node can be pinpointed by the sound made by the gamma ray counter. The surgeon makes an incision about 0.5 in long to remove the sentinel node. The blue dye that has been injected helps to verify that the surgeon is removing the right node. The incision is then closed and the tissue is sent to the hospital laboratory for examination.