Mole, other nevus – or could it be cancer?

It is a good idea to take a closer look at any areas of skin that have changed. That’s also true if an existing mole changes.

It can sometimes be difficult to tell the difference between melanomas and harmless moles (or other nevi). The following warning signs, often grouped together in the ABCDE rule, may be a sign of skin cancer:

• A (asymmetry): The spot or patch has an uneven, non-symmetrical shape.
• B (border): It has a frayed, jagged or fuzzy border that makes it difficult to tell where it ends and where the normal skin begins.
• C (color): It is a different color to the other moles – for example, especially dark – or has a mixture of different colors in it, such as light and dark brown shades, black or reddish areas.
• D (diameter): The spot or patch has a diameter of 5 millimeters or more.
• E (evolving): It gets bigger, changes color or starts bleeding, scabs over or itches. It may also stand out because it’s a little more raised than the surrounding skin.

People who notice any of these warning signs on a mole or other nevus should have it looked at by a dermatologist.

Your risk of melanoma skin cancer is higher if you have

• a lot of moles or other nevi caused by too much UV radiation, such as sunlight or tanning beds,
• dysplastic or atypical nevi, and
• very large nevi, with a diameter of over 20 centimeters.

Moles and other nevi are often already there from birth. Some of these aren't visible yet, but their foundations have been laid and they develop later. There are also nevi that arise later in life, known as acquired nevi. They are not there from birth, but develop mainly because the skin is exposed to sunlight (UV radiation) without protection. The more acquired nevi you have, the greater your risk of melanoma skin cancer. That’s why it’s important to to protect your skin from too much UV radiation.

Dysplastic nevi are benign (not cancer) but look similar to melanoma – perhaps because they have jagged edges or are an unusual color. “Dysplastic” means their cells have properties that are also found in pre-cancerous cells. But the only way to find out is to remove the nevus and examine it under a microscope.

Experts assume that people with dysplastic nevi have an increased risk of skin cancer. Then the cancer may also develop somewhere else on the skin (not just in those nevi). It is not possible to say exactly how likely they are to ever cause melanoma skin cancer. But the risk of cancer is thought to be especially high if you have a lot of dysplastic nevi due to genetic mutations. That is known as dysplastic nevus syndrome. People with this syndrome have more than 10 (sometimes even more than 100) dysplastic nevi spread over their body.

They are advised to have regular skin check-ups. So are people who have an increased risk of skin cancer for other reasons. If the doctor then notices that a mole or other nevus has changed, it is surgically removed.

It is rare for melanoma skin cancer to develop in a normal mole or other normal nevus. The risk is greater if you have very large congenital (at birth) nevi.

Experts believe that this is the case if the mole has a diameter of over 20 centimeters. Nevi with a diameter of over 40 centimeters – known as giant nevi – are particularly likely to turn into cancer. But nevi of that size are very rare.

Large congenital nevi are usually removed as a precaution. In children, this is done under general anesthesia. But it’s possible to wait until the child is a little older so a local anesthetic can be used instead. Until then, doctors keep a very close eye on the large nevus.