Histologically Diagnosed Dysplastic Naevi: A Patient Guide

Dr Chris Irwin

Figure 1. A normal naevus. Organised pigment cells within the rete ridges (the down projections of the epidermis) and organised dermal nests. Normal architecture (the cells organised in a normal way) and normal cells (no atypia).

Figure 2. Dysplastic naevus. Dysplastic naevi exhibit disorder of architecture (notice how they are no longer in neat little nests) and also disorder of cellular atypia (some of the individual cells are abnormal)

What is a Dysplastic Naevus?

A dysplastic naevus is a type of mole that appears benign (non-cancerous) but has some unusual features when examined under a microscope. The term comes from pathology: “dysplastic” means the cells look atypical or slightly abnormal (but not cancerous) in their arrangement or appearance, and “naevus” means a mole (a growth made of pigment-producing melanocyte cells). In other words, a dysplastic naevus is a mole where the microscopic structure is not entirely normal. Importantly, this is a histological diagnosis – it’s determined by a pathologist looking at a tissue sample under the microscope, rather than by appearance alone on the skin.

• How it’s different from a normal mole: Under the microscope, a dysplastic naevus shows an architectural disorder – the way the melanocyte cells are arranged in the skin is somewhat disorganized compared to a common mole. For example, the nests of melanocytes may spread out sideways beyond the main center of the mole (called “shouldering” or lateral extension) and might form bridges between neighboring rete ridges (the skin structures that project downward). There is often a thin band of fibrous tissue (scar-like collagen) underlying the mole (known as lamellar fibrosis) and a mild inflammatory response (a patchy lymphocytic infiltrate) around it. The mole’s cells (melanocytes) also show atypia, meaning the cell nuclei are a bit larger or irregular with darker staining than usual. These changes are less pronounced than what is seen in melanoma, but more than in an ordinary mole.
• How it’s different from an “atypical mole” diagnosed by sight: You may have heard the term atypical mole or Clark’s naevus used by doctors to describe a mole that looks unusual on the skin (for example, irregular in color or shape). While many dysplastic naevi do look atypical to the naked eye (often larger than normal moles, with irregular borders or mixed colors), not all do. In fact, many moles that are found to be “dysplastic” under the microscope can look perfectly ordinary on the skin. So, the diagnosis of a dysplastic naevus really comes from the microscope examination. In this handout, dysplastic naevus refers specifically to the histologically diagnosed lesion, not just any funny-looking mole on the skin.

What Causes Dysplastic Naevi and Who Gets Them?

Dysplastic naevi are thought to develop due to a mix of genetic factors and environmental influences:

• Genetics: Some people inherit a tendency to have multiple dysplastic moles. There is a familial condition (sometimes called atypical mole syndrome or FAMMM – Familial Atypical Multiple Mole Melanoma syndrome) where individuals have dozens of dysplastic naevi and a family history of melanoma. These people have a higher chance of developing melanoma in their lifetime. However, you do not need to have a family syndrome to develop dysplastic naevi – even without a strong family history, some individuals simply develop a few dysplastic moles due to their unique genetic makeup.
• Sun Exposure: Ultraviolet (UV) light from the sun (or tanning beds) is a known contributor to all types of moles and skin changes. Episodes of intense sun exposure or sunburns, especially in childhood, may increase the likelihood of developing atypical moles. Dysplastic naevi often appear in sun-exposed areas (like the back), but they can also occur in sun-protected areas, suggesting that sun is only part of the story. Protecting your skin from UV light can help reduce new moles and other skin damage.
• Skin Type: People with fair skin, light hair and eye color, and those who freckle easily tend to develop more moles (including atypical ones) than people with darker skin. However, dysplastic naevi can occur in anyone – having darker skin is somewhat protective but does not completely prevent dysplastic moles or melanoma.

Are Dysplastic Naevi Precancerous? (Understanding the Debate)

This is an important and sometimes confusing question. Dysplastic naevi have been at the center of a long debate among experts: are they early-stage melanoma waiting to happen, or are they just funny-looking benign moles? The truth lies somewhere in between and is still being studied:

• Not exactly “pre-cancer” in the way actinic keratoses are: An example of a true precancerous lesion is an actinic keratosis (a sun-damaged spot that can turn into a squamous cell carcinoma if not treated). Dysplastic naevi are not like that – the majority of dysplastic moles do not ever turn into melanoma. In fact, most melanomas (about 70-80%) seem to arise de novo (on their own on normal skin) rather than from an existing mole. Only rarely does a dysplastic naevus transform into a melanoma. So in that sense, we don’t consider every dysplastic mole a ticking time bomb of cancer.
• However, some may represent early changes toward melanoma: Particularly when a dysplastic naevus has high-grade atypia (see grading below), the line between a dysplastic naevus and an early melanoma in situ can be very fine. Pathologists sometimes even disagree on very severely atypical cases – one might call it “severely dysplastic naevus” while another might call the same sample “early melanoma.” 

There is no “magic test” to perfectly distinguish dysplastic naevi from melanoma – it is a decision made by an expert pathologist weighing a whole series of factors – and like anything based on human decisions – it is not perfect.

For these reasons, many doctors err on the side of caution with the dysplastic moles (treating them aggressively, as discussed in management). Historically, dysplastic naevi were even referred to as “Clark’s melanomas” by some researchers, implying they were a step along the pathway to melanoma. While that term isn’t used now, it highlights that in some cases a dysplastic naevus (especially a high-grade one) might be viewed as a very early melanoma or the stage ‘just before’ melanoma.

• A marker of risk (red flag) for melanoma: Perhaps the most accepted view today is that a histologically dysplastic naevus is more of a risk marker than a direct precursor. In other words, having these atypical moles on your skin indicates that your skin is the type that is prone to melanoma. The dysplastic naevus itself might never become cancerous, but the presence of dysplastic naevi increases the chance that somewhere on your skin, a melanoma could develop over time. We will discuss this risk in the next section.

In summary, experts continue to debate the exact nature of dysplastic naevi. They are benign moles by definition, but they are not entirely “normal” either. Think of them as warning signs that flag an increased risk, and in a few cases (especially if severely atypical) they might represent the very earliest stage in the melanoma spectrum. This uncertainty is why doctors generally choose to remove dysplastic naevi with margins when they are found – not because we think they are cancer, but because they could be hiding early cancerous changes or might cause confusion in the future.

Do Dysplastic Naevi Increase Melanoma Risk?

Yes. Having histologically confirmed dysplastic naevi is associated with a higher risk of melanoma developing in the future, and often that melanoma is an entirely new lesion (not the mole that was dysplastic, but elsewhere on the skin). Doctors consider patients with dysplastic moles to be in a higher risk category for melanoma.

• Overall risk: Studies have shown that people with multiple dysplastic naevi have a significantly elevated risk of melanoma compared to those without. For example, having more than five dysplastic moles may correspond to about a 10-fold increase in melanoma risk relative to someone with none. The Skin Cancer Foundation notes that individuals with 10 or more atypical moles might have roughly 12 times the risk of melanoma compared to someone without any. In practical terms, that means if your risk of melanoma was, say, 1 in 500 over a certain time, having many dysplastic moles could make it more like 1 in 50. It’s a marker that we need to be extra vigilant.
• Melanomas arising from dysplastic naevi: While most melanomas come out of the blue, a portion do seem to start where a dysplastic naevus is present. Experts estimate that about 20–30% of melanomas may develop in association with an atypical (dysplastic) mole. (One study cited about 1 in 4 melanomas arising from a dysplastic naevus.) This still means the majority of melanomas do not come from existing moles – they can appear on normal skin. So if you’ve had a dysplastic mole removed, it doesn’t mean you’re “safe” from melanoma in the future – you still need regular skin checks of your entire skin. Likewise, if you still have other moles, they should be watched.
• Family history and syndrome: If dysplastic naevi run in your family and especially if combined with a family history of melanoma, the risk is even higher. There’s a condition called dysplastic naevus syndrome where people have a very large number of these moles (often 100 or more) and a strong family incidence of melanoma. Such individuals have a very high lifetime risk of melanoma (50% or higher chance). Even if you don’t meet the criteria for that syndrome, having just a few dysplastic naevi means you should be more cautious with the sun and get regular skin exams.

Grading Dysplastic Naevi: Low-Grade vs High-Grade

Pathologists often describe how “atypical” a dysplastic naevus is by grading the degree of dysplasia (atypia) present. In the past, they used three tiers: mild, moderate, and severe dysplasia. However, this changed with the 2018 World Health Organization (WHO) Classification of Skin Tumours, which simplified the system into two tiers:

• Low-grade dysplastic naevus: This corresponds to the lesser degrees of atypia. In practice, a lesion that might have been called “moderately” dysplastic before would now often be simply termed low-grade. These have only mild to moderate cell atypia under the microscope. According to the WHO change, the category of “moderate” dysplasia was essentially eliminated as a separate label. Low-grade = moderate atypia in older terminology.
• High-grade dysplastic naevus: This corresponds to what pathologists used to call severely dysplastic naevus. High-grade means the cells look quite atypical (though still not blatantly cancerous) – often the nuclei are very enlarged, irregular and dark, approaching the appearance of melanoma in situ. The architecture may be very disorganized. In fact, a high-grade dysplastic naevus can be so atypical that some experts consider it essentially the same as a melanoma in situ, while others consider it a distinct (still benign) entity. High-grade = severe atypia in old terms.

According to an Australian pathology review in 2019, the WHO’s two-tier system removed the “mild” category and now we use only low-grade (≈ previously moderate) and high-grade (≈ previously severe) dysplasia. So if you compare:

• Old system: mild dysplasia, moderate dysplasia, severe dysplasia.
• New system: low-grade dysplastic naevus (covers what would have been mild or moderate), high-grade dysplastic naevus (covers severe).

The reason for this change is that the moderate category was somewhat subjective and pathologists did not always agree on what was moderate vs mild or severe. By simplifying it, the hope is to clarify management and get more agreement between doctors: basically, either the lesion is clearly low risk (low-grade) or it’s high risk (high-grade).

For you as a patient, the grade in the report gives an idea of how “close to melanoma” (or not) the mole appeared under the microscope, which in turn guides how your doctor manages it.

Treatment and Management of Dysplastic Naevi

When a dysplastic naevus is diagnosed on a skin biopsy or excision, the next steps depend on its grade and whether it was completely removed. The good news is that dysplastic naevi can be cured by complete removal – they do not “spread” if fully excised with a clear margin. The main question is how wide a margin is needed and whether additional treatment is prudent. Here’s how they are generally managed:

• Complete excision (surgical removal) is the standard for any confirmed dysplastic naevus. Your doctor will remove the mole along with a rim of normal skin around it to ensure the whole lesion is out. For a low-grade dysplastic naevus, this doesn’t require an aggressive surgery – usually a safety margin of about 2-3 mm of normal skin around the mole is considered sufficient.

• High-grade dysplastic naevus management: With high-grade lesions, doctors are more cautious. Because a high-grade dysplastic naevus can look so much like melanoma in situ under the microscope, the treatment approach is similar to melanoma in situ. That means ensuring adequate wide margins. Typically, if not already done, a re-excision with about a 5 mm margin of normal skin is recommended for a high-grade dysplastic naevus. This is the same margin recommended for melanoma in situ (which is the earliest form of melanoma confined to the top layer of skin). 

• Monitoring and follow-up: Removing a dysplastic naevus takes care of that mole, but because (as discussed) these moles are markers of risk, your doctor will likely recommend regular skin checks after that. Typically, if you’ve had one or a few low-grade dysplastic naevi, an annual full skin examination by a skin cancer doctor is advised – or more often if you have many of them or other risk factors. You should also perform monthly self-skin exams at home, keeping an eye on any changing moles or new lesions.

• Sun protection: As part of management, sun protection is essential. We can’t change our genes, but we can reduce environmental triggers. Diligent use of broad-spectrum sunscreen (SPF 50 or higher), wearing protective clothing and hats, and avoiding indoor tanning and midday sun exposure are all strongly recommended, especially if you have dysplastic naevi. Not only may this reduce the formation of new moles, but it will also lower your odds of getting melanoma and other skin cancers.

 It’s understandable to feel anxious when you hear that you have a “dysplastic” mole – the terminology can be scary. Remember that dysplastic naevi are extremely common and most never cause harm. We recommend removal and follow-up as a precaution and because we want to keep you safe in the long term. Having one dysplastic naevus does not mean you have skin cancer; it means we’re going to watch you a bit more closely to prevent skin cancer. Many people live a full life without ever developing melanoma, even if they have multiple dysplastic moles – especially with good monitoring and sun habits. So stay vigilant, but don’t lose peace of mind: with proper care, the risk can be managed.

References

1. National Cancer Institute (NCI). Common Moles, Dysplastic Naevi, and Risk of Melanoma. https://www.cancer.gov/types/skin/moles-fact-sheet#:~:text=Can%20a%20dysplastic%20nevus%20turn,into%20melanoma
2. Menzinger S. et al. “Dysplastic Naevi and Superficial Borderline Atypical Melanocytic Lesions: Description of an Algorithmic Clinico-Pathological Classification.” Dermatopathology (2025) https://pmc.ncbi.nlm.nih.gov/articles/PMC11860396/#:~:text=DN%20is%20often%20recognized%20as,4%20%2C%2025%2C6%20%2C%2027
3. Skin Cancer Foundation. Atypical Moles & Your Skin – The Facts, The Risks, How They Affect You. (2022) https://www.skincancer.org/risk-factors/atypical-moles/#:~:text=People%20with%2010%20or%20more,12x%20THE%20RISK%20OF%20MELANOMA
4. Calabresi L. “Dysplastic naevi: the controversy continues.” Healthed Clinical Articles (May 8, 2019) healthed.com.au
5. Libre Pathology Wiki. “Dysplastic nevus.” (2021) https://librepathology.org/wiki/Dysplastic_nevus#:~:text=,The