American Melanoma Institute · 5 min read
What doctors mean by atypical or dysplastic moles, how pathology grading affects re-excision, and what these moles say about melanoma risk.
Few terms in dermatology cause as much confusion as atypical mole and dysplastic nevus. Patients hear them and assume precancer. Doctors use them in 2 different ways, one in the exam room and one at the microscope, and the 2 meanings don't always line up.
About 1 in 10 Americans has at least 1 such mole, according to the National Cancer Institute. Nevus (plural nevi) is simply the medical word for a mole.
In the exam room, atypical describes appearance. An atypical mole is usually wider than 5 mm, has an irregular or fuzzy edge that fades into the surrounding skin, and carries a mix of colors from pink to dark brown. Many are flat with a raised center, a shape often compared to a fried egg.
These features overlap with the ABCDE warning signs of melanoma, which is why atypical moles draw attention. An unusual look marks a mole as worth watching, and sometimes worth sampling. Most of them stay harmless for life.
When a mole is removed, a pathologist examines it. Dysplastic refers to a specific set of microscopic findings. These include pigment cells spreading in a disordered pattern along the base of the epidermis, nests of cells that bridge between neighboring skin ridges, cells with enlarged or darker nuclei (cytologic atypia), and an immune and scarring reaction in the dermis underneath.
DermNet makes a point that surprises many people: only a minority of moles that look atypical meet the microscopic criteria for a dysplastic nevus, and many moles that look ordinary turn out to be dysplastic under the microscope. The 2 terms are therefore not interchangeable. A dysplastic nevus is a benign mole.
Many pathologists grade the degree of atypia as mild, moderate, or severe, based on how abnormal the cells and their arrangement appear. Some laboratories use 2 tiers instead, low grade and high grade.
Grading is a judgment call, and pathologists don't always agree with one another, especially in the middle of the scale. Severely dysplastic nevi sit closest to melanoma in situ in appearance.
Your report will also state whether the mole reached the edge of the sample, called a positive margin, or whether the margins were clear. The grade and the margin status together drive the next decision.
In 2015, a group of pigmented lesion specialists published a consensus statement in JAMA Dermatology (Kim and colleagues, the Pigmented Lesion Subcommittee of the Melanoma Prevention Working Group). Their recommendations:
More data arrived in 2018. A study from 9 US academic centers, also led by Kim and published in JAMA Dermatology, followed 467 moderately dysplastic nevi that had positive margins and were not re-excised. After an average of 6.9 years, none had turned into melanoma at the biopsy site. The authors concluded that observation with routine skin checks is a reasonable approach.
Severely dysplastic nevi are handled differently. Because they can be hard to tell apart from early melanoma, many authors recommend re-excision to be sure the entire mole is out. Doctors also tend to re-excise when pigment remains or returns in the scar, or when the pathologist cannot rule out melanoma.
People often mix 2 separate questions together. The first is whether a given dysplastic nevus will become melanoma. The National Cancer Institute's answer: only rarely. Most melanomas do not start in a mole of any kind, and doctors do not recommend removing every atypical mole as a preventive step.
The second question is what the moles say about the person, and here the numbers are larger. The National Cancer Institute reports that someone with more than 5 dysplastic nevi has about 10 times the melanoma risk of someone with none. In the 2018 study, none of the biopsy sites developed melanoma, yet about 23% of the patients developed a melanoma somewhere else on their skin during follow-up. A previous melanoma was the strongest predictor. The mole serves mainly as a marker of the person's risk.
Risk is highest in families with FAMMM (familial atypical multiple mole melanoma) syndrome, in which a person has more than 50 moles and at least 1 close relative has had melanoma. Some of these families carry a mutation in a gene called CDKN2A, and genetic counseling may be offered.
For people with dysplastic nevi, the National Cancer Institute suggests a monthly self-check and a skin exam by a doctor about once a year, or every 3 to 6 months when there is a family history of melanoma.
Dermatologists have tools that make watching safer than it sounds. Total body photography (sometimes called mole mapping) creates a baseline record of the skin, so that a new or changed mole stands out at the next visit. Dermoscopy, a handheld magnifier with its own light, reveals pigment patterns below the surface, and stored dermoscopic images of a single mole can be compared over time. A stable mole can stay. A mole that changes gets removed.
At home, the ugly duckling rule is useful. People with many atypical moles usually have a signature pattern, and their moles resemble one another. The mole that breaks the pattern is the one to point out.
