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Sentinel Node Mapping for Melanoma

When you have melanoma, the most dangerous type of skin cancer, it's crucial to know whether it has spread from its original site to other places in your body. This helps determine the stage of your cancer, an important step in figuring out the best treatment approach.

If the melanoma is of a certain thickness and size, or has other concerning features, your doctor may recommend sentinel node mapping. This is because once the cancer has grown deeply enough into the skin, it can travel to a nearby lymph node, and the first place the cancer tends to spread is the lymph node or nodes that are closest to it.

This node (or group of nodes) is called a sentinel node because it sounds the alarm that the cancer has begun to spread. After cancer invades lymph nodes, it can spread through the body's lymphatic system, a network that transports clear lymph fluid, bringing protein, fats, and water from tissues to the bloodstream.

Doctors used to try to find out about whether cancer had spread by removing lymph nodes near to the original cancer site during surgery to remove the cancer itself. The doctors then sent the lymph nodes to a lab for a biopsy, to find out whether any cancer cells were present. This approach meant that, for many patients, surgeons took out more lymph nodes than necessary, which often increased the risk of unpleasant side effects like lymphedema. Lymphedema is a chronic, debilitating swelling in the arms or legs resulting from damage to the lymphatic system.

Now, doctors use an approach called sentinel node mapping. This is a technique that allows surgeons to find the specific lymph nodes that cancer is likely to travel to first—instead of all the lymph nodes nearby—and then biopsy only one or a few of the most likely nodes. Studies have shown that this approach is safe and effective for the majority of patients and that it works best if it is done before or during any surgery to remove the cancer.

How sentinel node mapping is done

During surgery to remove the cancer cells, your surgeon will inject a radioactive substance and possibly a blue dye into the site of your melanoma. Then he or she will wait for about an hour or so while the substance and dye spread. Using a tool that detects radioactivity, your surgeon will follow the path of the dye to one or more lymph nodes, which are then considered most probable to have cancer cells (if your cancer has spread). This is how the surgeon finds the lymph nodes that could be biopsied as part of your cancer diagnosis and treatment.

If the lymph node or nodes don't contain cancer cells, the surgeon will leave the rest of the lymph nodes alone. Studies have shown that if the sentinel node or nodes are negative for cancer, then the remaining lymph nodes are likely to be cancer-free as well.

If the lymph node does contain cancer cells, the surgeon may want to biopsy more lymph nodes in the area to find out how far the cancer cells might have spread.

If there are any lymph nodes in the area that are unusually large, they may be biopsied without the dye and imaging procedure.

Risks of this procedure include false negative results in about 2 percent of patients. This means that, in these rare cases, lymph nodes that have cancer are missed.

The most common complications are wound infection, lymphedema, or a hematoma, which is a localized swelling filled with blood. But these complications are far more likely in people undergoing removal of many or all lymph nodes in the tumor area.

This surgery generally requires you to be sedated by intravenous (IV) or general anesthesia. It is typically performed on an inpatient basis, which means that you may need to stay overnight to recover from the procedure.