Atypical Mole.

A Mole sent for pathology usually turns out to be a “dyplastic nevus” rather than a melanoma.

What is an Atypical Mole?

An atypical mole (dysplastic nevus) is a mole that looks more concerning than a simple nevus.

Put Simply, an atypical mole:

  • Is not a “normal looking mole”
  • Is not a melanoma
  • Causes concern for patients
  • Makes the skin cancer doctor “stop” in their tracks

An Atypical mole may be larger, darker, have a greater range of colours, or have an irregular border – any of the ABCD features of a melanoma.

It is extremely difficult for a layperson to distinguish dysplastic nevi from a melanoma. Furthermore, around 25% of melanoma occurs from an existing mole.

Regular screenings at a skin cancer clinic are key to monitoring dysplastic nevi and early detection of melanoma. Dermoscopy is very helpful but it may still not be possible for the doctor to call a lesion either a melanoma or dysplastic nevus without doing a biopsy. There are even times when a melanoma is hidden within the perimeter of dysplastic nevi.

The term dysplastic nevus is often used by dermatopathologists, and the term atypical nevus most often used by clinicians.

It comes as a surprise for most people to hear that it is often difficult for histopathologists to distinguish a melanoma from a dysplastic nevus. A “Severely dysplastic nevus” is generally regarded as a melanoma in all but name.

Do Atypical Moles matter?

Up to four atypical nevi are regarded as normal. More than 10 atypical moles in someone in a melanoma-prone family might well indicate the Familial Atypical Mole & Melanoma Syndrome (FAMM syndrome).  People with the FAMM are at much greater risk of developing melanoma. Another term similar to FAMM syndrome is dysplastic nevus syndrome.

The way to look at it, though, is that atypical moles are a “risk factor” for developing a melanoma. Someone with large numbers of  “Normal” looking moles is also at increased risk of melanoma.

The risk of melanoma:

  • in a person with more than 100 moles is around seven times greater
  • in a person with more than 5 Atypical moles is around ten times greater

The risk is not an absolute “increase” or “no increase” – rather, the risk of melanoma increases continually with greater numbers of moles and atypical moles.

Someone with FAMM syndrome will benefit from the diagnosis because of the strong indication for regular skin checks and monitoring. However, someone with lots of moles and/or several atypical moles will also benefit from regular skin checks even without the full diagnostic criteria for FAMM syndrome.

Atypical moles are also significant simply because they may look like a melanoma and need dermatoscopic monitoring or even biopsy.

More than 10 atypical moles in someone in a melanoma-prone family might well indicate the Familial Atypical Mole & Melanoma Syndrome (FAMM syndrome)

There is also an association between the number of atypical moles a person has and the risk of thicker melanoma. This was found in a study of 566 people with atypical moles that was published in 2016. The authors state that “Younger patients should be educated on the increased risk of thicker melanomas that is associated with having more atypical nevi (moles).” It also is appropriate to consider a more frequent skin check.

What does  an Atypical Mole Look like?

The following features are often used to determine if a mole is atypical:

  • Size: 5mm or more in diameter
  • Color: variable eg. different shades of brown, black or red
  • Edge: Irregular
  • Surface: might be slightly cobblestoned or pebbly in texture
  • Difference between nevi: There tends to be a wider range than normal of different nevi appearances – varying in size, color, edge, surface for example.
  • Background skin shows numerous nevi – often more than 50

Of course the key condition to exclude is a melanoma because the features of a melanoma.