Sentinel Lymph Node Mapping Health Article

Definition

Sentinel lymph node mapping is a method of determining whether cancer has metastasized (spread) beyond the primary tumor and into the lymph system. The mapping procedure is used in conjunction with sentinel lymph node biopsy or dissection.

Purpose

The lymph system is the body's primary defense against infection. Lymph vessels carry clear, slightly yellow fluid called lymph that contains and proteins to help rid the body of infection. Lymph nodes are small, bean-shaped collections of tissue found along the lymph vessels. Cancer cells can break off from the original tumor and spread through the lymph system to distant parts of the body where secondary tumors are formed. One job of the lymph nodes is to clean the lymph by trapping foreign cells, such as bacteria or cancer cells, and identifying foreign proteins for antibody response.

The sentinel lymph node is the first lymph node that filters the fluid draining away from the primary tumor. If cancer cells are breaking off and entering the lymph system, the first filtering node (not necessarily the closest to the tumor) will be most likely to contain the breakaway cancer cells.

There are about 600 lymph nodes in the body. About 200 are in the head and neck and another 30-50 are in the armpit. Others are located in the groin. The sentinel node, or first filtering lymph node, will be different for each tumor and for each individual. Sentinel lymph node mapping is a technique for pinpointing which node is the most likely to receive the primary drainage from the tumor and therefore the most likely to contain cancer, so that it can be surgically removed and examined under the microscope for cancer.

If the sentinel node is cancer-free, there is a very high probability that cancer has not spread to any other node. If cancer cells are present in the sentinel node, it is likely that other nodes in the lymph system also contain cancer cells. This information is important in staging the cancer and individualizing cancer treatment for maximum benefit.

Sentinel lymph node mapping is a relatively new technique. It was first used in 1977 by researchers studying cancer of the penis. Later it was used successfully in staging melanoma (a type of skin cancer). In 1993, researchers first used the technique in breast cancer patients. Since then, clinical trials in breast cancer patients have demonstrated the accuracy and effectiveness of sentinel lymph node mapping and dissection in the staging of breast cancer. Researchers hope to be able to apply the sentinel node technique to other cancers in the future.

Advantages of sentinel lymph node mapping

Before sentinel node mapping was developed, there was no way of knowing whether and how far cancer had spread without removing and examining samples from many lymph nodes under the microscope. For example, in breast cancer patients, after a lumpectomy or mastectomy it was conventional treatment to remove most of the axillary nodes. These are the lymph nodes in the armpit. Removing axillary nodes causes frequent complications in as many as 80% of women. These complications include swelling (lymphedema), numbness, burning sensation in the armpit, reduction in arm and shoulder movement, and increased risk of infection.

Sentinel lymph node dissection limits the extent of surgery. It provides the following advantages:

• Less surgical trauma because only one lymph node or a small cluster of nodes is removed. For example, in breast cancers, two or three nodes are generally removed.
• Fewer side effects from surgery.
• The lymph system is left intact and is better able to transport fluid and fight infection.
• Fewer risks of impairment of arm and shoulder movements.
• With only a small amount of tissue being removed, it can be studied much more exhaustively in the laboratory for the presence of cancer.
• Significant reduction in post-mastectomy pain.

How accurate are sentinel lymph node mapping and dissection?

In 2001, sentinel lymph node mapping is being used primarily in cases of melanoma and breast cancer. The technique is relatively new, and several breast cancer clinical trials are underway. One purpose is to determine the most accurate methods of finding the sentinel node. Another is to compare the control of cancer and survival rates of sentinel node biopsy with conventional axillary lymph node dissection in women whose sentinel nodes are both positive and negative for cancer. Up-to-date information about these clinical trials can be obtained from the National Cancer Institute at <http://www.cancertrials.nci.nih.gov> or (800) 4-CANCER.

Since sentinel lymph node mapping and dissection are relatively new, they are not done at every hospital. Doctors need special training in order to perform these procedures. Studies consistently have shown that the ability to locate the sentinel node increases the more experience doctors have with the procedure. Experienced physicians can pinpoint the sentinel node with about 95% to 98% accuracy. Similarly, studies have shown that there is a learning curve for surgeons and pathologists (doctors who examine the nodes in the laboratory) in sentinel lymph node dissection. The more experience they have, the more accurate they are.

Overall, accurate diagnoses from sentinel lymph node dissection are very high (92% or more). However, it is important that the patient find out how much training and experience the treatment team has with this procedure, and if necessary ask for a referral to another facility with more experienced staff. Some insurers may also consider the procedure experimental. Patients should check with their insurers about coverage, as the acceptance of this procedure is evolving.