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Sentinel Node Mapping: A Special Technique for Detecting the Spread of Melanoma

After diagnosis, one of the most difficult times for people with cancer is the long wait to hear whether their cancer has spread. Everything depends on it - their course of treatment, their quality of life, even their survival.

This is particularly true if you have melanoma of the skin. This type of skin cancer is highly curable in its early stages, but it is much more difficult to treat once it has spread to other parts of the body.

Until recently, finding out whether melanoma had spread often required major surgery to remove lymph nodes near the melanoma. This sometimes left people with many short- and long-term complications, such as pain and swelling. Now, though, a technique called sentinel node biopsy offers an accurate diagnosis while sparing many people a long recovery with side effects.

How Melanoma Used to Be Treated

Surgeons first remove the melanoma from the skin. In the past, if the cancer was large enough, they would then remove the nearby lymph nodes for testing. That’s because cancer tends to travel to lymph nodes first. When melanoma was found on a person’s arm, for example, doctors would remove lymph nodes in the armpit. Then doctors would check the lymph nodes for cancer in the lab. There are so many lymph nodes in a person’s body, however, that it wasn’t always possible to predict which lymph nodes the melanoma might spread to.

Doctors soon began to wonder whether lymph node removal was the best method. Removing lymph nodes can cause scarring, nerve damage, and lymphedema - a painful swelling of the arms or legs.

A new approach for identifying involved lymph nodes came in the 1990s with the sentinel lymph node evaluation technique. First used in people with melanoma, this technique is now also being used in women with breast cancer to see whether the disease has spread beyond the breast.

What Lymph Nodes Are

Unlike more active body parts, such as the heart or brain, the lymph system plugs along quietly, keeping cells clean and germ-free. If you’ve ever popped a blister, you’ve seen lymph. It’s the clear liquid that leaks out, which is rich in germ-fighting cells.

The lymph system is a network of small lymph streams. These streams drain through channels down the arms and legs and other parts of the body into major junctions called lymph nodes. Within these lymph nodes, special cells clean out cell waste, bacteria, and even cancer cells. Because channels connect the lymph nodes, cancer can invade other nodes and parts of the body once it is established in one lymph node. When this happens, melanoma and other cancers are much more difficult to treat, and survival dips.

Sentinel Node Biopsy

The sentinel node is so named because it is where cancer first arrives from the original tumor site. It is the most likely node to contain cancer if the cancer has spread to the nodes.

Surgeons hunt for the sentinel lymph node using a radioactive tracer, blue dye, or both. Using both the tracer and dye ensures the greatest success in finding the sentinel node. The surgeon injects the tracer around the tumor site. It follows the route of the tumor’s drainage. Then the surgeon uses a scanner to find the “hot spot” where the radiation is concentrated. The doctor may also inject blue dye around the tumor site and then look for the node that is dyed blue. There may be more than one sentinel node. Surgeons will remove any suspicious nodes and send them to a specialist trained to look for cancer cells, called a pathologist.

If the sentinel node is positive, surgeons generally remove all the nodes in the area because there is a small chance the cancer has traveled to other nodes in that same region. But if the sentinel node is cancer-free, doctors leave the remaining nodes in place.

Deciding on Treatment

If nodes are cancer-free, people usually do not need further treatment. However, it is possible that some people will have cancer recurrence even with negative nodes.

Experts say that people with initial positive biopsies are at greatest risk for melanoma spread or recurrence. Most people will have the rest of their nodes removed. However, there is no evidence right now that removing all lymph nodes improves survival. To improve treatment success, people with melanoma that has spread may also have immunotherapy, chemotherapy, radiation therapy, or combinations of these treatments.

Where to Go for Care

Major cancer centers have specialists in treating melanoma. When looking for a melanoma specialist, patients should ask questions such as these:

  • Do you or a surgeon you work with regularly perform sentinel node biopsies or lymphatic mapping for melanoma?

  • Do you treat patients yourself or refer them to a larger center?

  • Do you offer any clinical trials for melanoma and have you published any reports of their results?