How Moles Turn Into Melanoma

People with more moles are more likely to develop melanoma, the deadliest form of skin cancer. However, why a formerly benign mole changes into cancer has remained much of a mystery. Also up for debate was whether or not an “intermediate” stage exists (the stage between a normal mole and melanoma).

It turns out that such a stage does exist, and examining the genetic mutations in a mole can determine whether it may soon progress into cancer. While all moles contain genetic mutations, most of them are harmless.

After analyzing tumor DNA and comparing to healthy-tissue DNA, however, researchers found that melanomas had additional genetic mutations. Not only did the mutations tend to increase with time, but even the areas of the mole that were not yet cancerous had extra mutations. As reported by NBC News:

“What we have shown is those alterations can be found in the benign precursors,” [study author Dr. Boris] Bastian said. That means melanoma is similar to other forms of cancer, such as colon cancer or cervical cancer, which start with benign growths that can progress to cancer.”

Specifically, normal moles are known to carry a mutation called BRAF V600E. In moles that later became cancerous, an increasing number of mutations were acquired. Of note, the additional mutations are thought to be caused by exposure to ultraviolet light.

The discovery could be game changing for the diagnosis and treatment of skin cancer. Currently, dermatologists remove any moles that are deemed suspicious. Genetic testing could one day be used to determine which moles are at risk of turning cancerous.

This way, if a mole has mutations that suggest it may turn into melanoma, it could be removed along with extra surrounding tissue and/or additional testing to find out if cancer had already spread to the lymph nodes. The researchers concluded:

“Our study defined the succession of genetic alterations during melanoma progression, showing distinct evolutionary trajectories for different melanoma subtypes.

It identified an intermediate category of melanocytic neoplasia, characterized by the presence of more than one pathogenic genetic alteration and distinctive histopathological features.

Finally, our study implicated ultraviolet radiation as a major factor in both the initiation and progression of melanoma.”

Genetic testing such as this may one day help doctors detect melanoma earlier, improving treatment and survival rates. However, in the meantime you should have your skin regularly checked by a doctor.

Be on the lookout, in particular, for any new or unusual spots on your skin. The American Cancer Society recommends using the ABCDE guide to help you spot potential signs of melanoma. If you notice any of the following, see your doctor right away:

A: Asymmetry: One half of a mole or birthmark does not match the other.

B: Border:The edges are irregular, ragged, notched, or blurred.

C: Color:The color is not the same all over and may include shades of brown or black, or sometimes with patches of pink, red, white, or blue.

D: Diameter:The spot is larger than 6 millimeters across (about ¼ inch – the size of a pencil eraser), although melanomas can sometimes be smaller than this.

E: Evolving: The mole is changing in size, shape, or color.

Sources

New England Journal of Medicine November 12, 2015
NBC News November 13, 2015