What appears to be a mole growing on top of another can be melanoma.

“It would be rare but not impossible for one mole to grow within another mole,” says Estee Williams, MD, a board certified medical, cosmetic and surgical dermatologist and assistant clinical professor in dermatology at Mount Sinai Medical Center.

Dr. Williams adds, “Certainly this would constitute a change in the mole, and should be checked in person by a dermatologist.”

That’s the key word: change. Have you known the mole to be on top of, or apparently within, a bigger mole for as long as you can remember?

If so, has the duo changed in appearance? If not, it’s probably as benign as it was years ago.

The medical term for mole is nevus (plural: nevi).

If you’ve always had one mole on top of another, is one of the moles looking different lately?

If so, you need to have a dermatologist inspect it – with a dermatoscope.

Shutterstock/Erica Smit

A mole can change into melanoma, as you certainly already know. And a melanoma can arise on top of a mole, and in its early stage of growth, the cancer can resemble a common mole.

But the fact that a benign mole sits on top of or inside of another normal nevus does not make either nevus more likely to commence a malignant transformation. It’s a location thing, not a DNA mutation thing.

In other words, just because a mole is on top of another doesn’t mean it’s atypical.

An atypical nevus, however, can be located anywhere and is made up of atypical cells.

These nevi have an odd or irregular appearance but are benign. Atypia means that the benign mole is simply more likely than a nearby typical mole to ever transform into melanoma. The issue is “more likely to,” not “destined to.”

Dr. Williams’ clinic offers serial digital dermoscopy – computer based mole mapping – to track one’s nevi for changes over time.

Serial digital dermoscopy

The images are compared to the patient’s previous images for telltale signs of evolution.

The images are also rated by the computer’s algorithm for an index of melanoma suspicion. If the index is high, a biopsy will be recommended.

When a normal or common appearing mole sits on top of another typical looking nevus, this “stacking,” in and of itself, is not a reason to pay extra close attention when you do your monthly skin exams – beyond what is necessary simply to get a good look at the duo.

But remember, if this duo is a new phenomenon, have it checked out!

Dr. Williams strives to be at the forefront of her field, being active in local, national and international medical and cosmetic dermatology conferences. 
Lorra Garrick has been covering medical, fitness and cybersecurity topics for many years, having written thousands of articles for print magazines and websites, including as a ghostwriter. She’s also a former ACE-certified personal trainer.


Top image: Shutterstock/pixinoo