Melanoma is the least common form of skin cancer, but it's considered the most dangerous type. That's because melanomas tend to spread to other parts of the body, and once they've done so, it's difficult to treat them successfully.
Fortunately, the majority of melanomas are diagnosed and treated before they've had a chance to start spreading down into the deeper layers of the skin, and from there to other parts of the body. In fact, most melanomas take years to start spreading downward, although a minority of them start spreading quite early.
Treatment of melanoma depends on the following factors, all of which are included in the staging of melanoma:
Thickness of the melanoma: The depth of the thickest part of the melanoma is an important part of staging melanoma. Treatment varies depending on the stage at diagnosis. The thickness of the melanoma also corresponds to prognosis: Thinner melanomas (less than 2 millimeters thick) have good cure rates, whereas thicker melanomas (4 or more millimeters thick) are more likely to spread and cause death.
Whether the melanoma has spread to nearby lymph nodes: When melanoma spreads, it tends to start by going to nearby lymph nodes. Doctors usually biopsy nearby lymph nodes if the melanoma has a thickness of one millimeter or more.
Whether the melanoma has spread to further parts of the body: After spreading to lymph nodes, some melanomas may spread to other parts of the body. If melanoma is found in the lymph nodes, or if there are other symptoms concerning for metastatic spread to other parts of the body, doctors can check for spread with CT scans, MRI scans, or PET scans.
Depending on the factors above, melanoma is treated with one or more of the following techniques:
Virtually all melanoma treatment starts with a "wide" surgical excision: The original melanoma is surgically removed from the skin, usually under local anesthesia. The surgery includes the removal of 1 to 2 centimeters of normal skin around the melanoma and should go down to the deepest layer of the skin. This "wide" excision is done to minimize the chance that any stray tumor cells are left behind. (Note: Surgeons used to take up to five millimeters of normal skin with the melanoma; however, research studies found that there's no benefit in taking more than two millimeters.)
For thinner melanomas, a wide excision is often curative. However, in a minority of cases, the melanoma may recur in the same spot.
Lymph node biopsy
If the melanoma is more than one millimeter thick, or if there are other reasons to suspect possible spread to the lymph nodes, doctors will biopsy nearby lymph nodes to check for spread. To identify the lymph nodes to which cancer cells are most likely to spread, they may use a procedure known as "sentinel lymph node biopsy." This involves injecting a mildly radioactive tracing compound into the skin near the melanoma location, then using special imaging to follow the tracer into a nearby lymph node.
Complete lymph node dissection
This process of removing a large cluster of lymph nodes is usually done when lymph node biopsy is positive, or if there are other signs of spread to the lymph nodes.
After surgical removal of lymph nodes, there still remains a 30 to 80 percent chance of the melanoma recurring eventually. To reduce the chance of recurrence, most experts recommend a course of interferon alfa. This special compound is a form of "immunotherapy" that involves intravenous or subcutaneous injections of a protein that modulates the body's immune system and tends to interfere with tumor growth. Because treatment with interferon usually takes a year and is associated with significant side effects, it's usually only recommended for patients who are in good health and otherwise likely to live ten years or more.
Radiation is only rarely used for the initial treatment for melanoma; it's more often used for palliative purposes in incurable melanoma. In particular, it can be used to reduce pain and symptoms from melanoma that may have spread to the spine or bones. Occasionally, though, radiation is used after surgical removal of melanoma or nearby lymph nodes in an attempt to reduce the chance of the melanoma recurring.
Treatments for advanced melanoma
Unfortunately, advanced melanoma that has spread throughout the body is very difficult to cure. Research is ongoing, and the most promising approaches involve treating patients with strong immunotherapy compounds (drugs that interfere with certain immune system pathways). Surgery and radiation may also be attempted, although usually the goal is pain and symptom relief rather than cure.
See also the FAQs How is skin cancer staged? and What kind of follow-up should I have after treatment for skin cancer?