Sentinel Node Biopsy
Sentinel Node Biopsy Overview
Sentinel node biopsy is a surgical procedure that doctors use to stage (determine the extent of spread of) certain types of cancer in patients who have been recently diagnosed with cancer. Sentinel node biopsy is most commonly associated with staging breast cancer; however, the procedure is also commonly used to stage malignant melanoma (a type of skin cancer). Sentinel node biopsy may also be called sentinel lymph node biopsy or sentinel lymph node dissection.
Lymph nodes are pea-sized structures that filter fluids that circulate through the body. The lymph nodes collect foreign materials such as cancer cells, bacteria, and viruses from these fluids. White blood cells, which are components of the immune system, attack the collected foreign material in the lymph nodes. Malignant (cancerous) tumors such as breast cancers may grow and spread enough that the lymph and blood vessels that run through the breast begin to circulate the cancer's cells through the body, and they may begin to grow in other locations as a result. Most cancerous breast tumors drain to the group of lymph nodes in the underarm closest to the growing tumor.
The first node that the fluid passes through in a group of lymph nodes is called the sentinel lymph node. The term sentinel is derived from the French word sentinelle, which means "to guard over" or "vigilance." Thus, the sentinel lymph node is the protective node that acts as the first filter of harmful materials.
During a sentinel lymph node biopsy, the surgeon usually removes one to five sentinel lymph nodes (from an underarm if breast cancer is involved) and sends those nodes for examination by a pathologist to determine if cancer cells have spread to them. If cancer cells are found in these lymph nodes, it means that the cancer might be metastasizing (spreading through the body). Therefore, a sentinel node biopsy is an important tool for doctors to use in determining what further treatment is necessary for the cancer as well as determining the patient's prognosis.
Sentinel node biopsy has been in use for almost 10 years. The traditional procedure for staging breast cancer used to be a surgery called axillary lymph node dissection (ALND), which involves removing most (usually 10-30) of the lymph nodes in the armpit closest to the breast tumor. The benefit of ALND is that all of the lymph nodes can be examined for the presence of cancer cells, and the doctor can use those findings to make a reliable determination of whether the cancer is spreading.
The drawback of ALND is that the procedure is associated with postsurgical complications such as movement problems in the shoulder, wound infection, nerve damage, and lymphedema. Lymphedema is swelling, most often in the arms and legs, caused by accumulation of lymphatic fluid (fluid that helps fight infection and disease). Only 10%-20% of women who undergo an ALND develop lymphedema, but it can be a serious, untreatable condition that involves painful and chronic (long-term) swelling of the arm.
By design a less-invasive method to stage breast cancer than ALND, sentinel node biopsy is associated with fewer complications that may develop after the procedure. Instead of all of the lymph nodes being removed, sentinel node biopsy involves removing an average of two to three lymph nodes. Compared to ALND, sentinel node biopsy usually takes less time to perform, is less painful, requires a much smaller incision, and is associated with a shorter recovery period. The main argument in support of sentinel node biopsy is that if no cancer has spread to the sentinel lymph nodes, removal of the remaining lymph nodes is not warranted. Doing so would only increase the risk of postsurgical complications without providing further benefits.
In addition, the accuracy involved with a sentinel node biopsy is comparable or better to those of ALND. Surgeons who are accustomed to the procedure can identify the sentinel lymph node in 85%-98% of patients. They can also accurately determine if the cancer is spreading in 95% of patients. The false-negative rate (percentage of cases in which no cancer cells are found in the sentinel lymph node but are present in "downstream" nodes) is less than 5%.
The way the pathologist processes and evaluates sentinel lymph nodes is different from how they would evaluate the nodes retrieved in an axillary dissection. Specifically, the pathologist looks at many more portions of the sentinel node and may perform special studies to enhance the ability to identify cancer cells on those nodes. This provides a more in-depth look at each sentinel node.
Leigh A Neumayer, MD, MS, FACS
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