Understanding Dysplastic Nevi (Atypical Moles) and Severely Dysplastic Nevi

Prepared by: SimcoDerm Medical & Surgical Dermatology Centre

Your Biopsy Result

Your skin biopsy showed a dysplastic nevus (atypical mole) or a severely dysplastic nevus.

Hearing these terms can be worrying, especially because they contain words like “atypical” or “severe.” Fortunately, these lesions are not the same as invasive melanoma (skin cancer), and in most cases they can be treated successfully.

This Handout Explains

What a dysplastic nevus is
Why it develops
The difference between a dysplastic nevus and a severely dysplastic nevus
Why some lesions require additional surgery
What happens next
How to reduce your future risk

What is a Mole (Nevus)?

A mole, also called a nevus, is a collection of pigment-producing cells called melanocytes.

Melanocytes normally give your skin its color and help protect it from ultraviolet (UV) radiation from the sun.

Sometimes these cells grow together in a small area, forming a mole.

Most adults have 10–40 moles, and many are completely harmless.

What is a Dysplastic Nevus?

A dysplastic nevus (also called an atypical mole) is a mole whose cells look slightly abnormal under the microscope.

This does NOT mean you have melanoma.

Instead, it means that the melanocytes have developed some abnormal changes that are greater than those seen in a normal mole but not enough to be considered melanoma.

Think of it as a mole that has started to change but has not become skin cancer.

Why Do Dysplastic Nevi Develop?

There is no single cause, but several factors increase the chance of developing dysplastic moles.

1. Sun Exposure (The Most Important Cause)

Ultraviolet (UV) rays from the sun or tanning beds damage the DNA inside skin cells.

Normally, your body repairs this damage.

However, after years of repeated sun exposure, some pigment cells accumulate permanent DNA damage.

These damaged melanocytes may begin to grow differently and develop into a dysplastic nevus.

This is why dysplastic nevi are commonly found on areas that receive significant sun exposure such as:

Back
Chest
Arms
Legs
Face

2. Genetics

Some people naturally develop many atypical moles because of inherited genes.

If several family members have many atypical moles or melanoma, your risk is higher.

3. Fair Skin

People with:

fair skin
blue or green eyes
blond or red hair
freckles

are more likely to develop dysplastic nevi because their skin is more easily damaged by UV radiation.

Is a Dysplastic Nevus Cancer?

No.

A dysplastic nevus is not melanoma.

However, it is considered a precancerous change because it has some abnormal features.

Most dysplastic nevi never become melanoma.

Many remain unchanged for life.

Others may slowly disappear.

Only a small percentage progress further.

What Did My Biopsy Show?

The pathologist examined your biopsy under a microscope.

They look at how abnormal the melanocytes appear.

The abnormality is often described as:

Mild dysplasia
Moderate dysplasia
Severe dysplasia

The greater the degree of abnormality, the greater the concern.

If Your Pathology Shows a Dysplastic Nevus

Good news.

If the biopsy has completely removed the lesion (the pathology report says the lesion is completely excised or the margins are clear), then:

No further treatment is usually needed.

The abnormal mole has already been removed.

There is nothing left to treat.

What Happens Next?

You simply continue with:

routine skin examinations
regular follow-up with your dermatologist
monthly skin self-examinations
lifelong sun protection

The biopsy site will heal with a small scar that may remain for a long period.

The dysplastic nevus itself is gone.

Why Is Follow-up Still Important?

Having one dysplastic nevus means your skin has shown it can develop atypical moles.

This does not mean you will develop melanoma.

However, it does mean you have a slightly higher lifetime risk than someone who has never had one.

Regular skin examinations help detect any new suspicious lesions early.

What is a Severely Dysplastic Nevus?

A severely dysplastic nevus is different.

Under the microscope, the melanocytes look much more abnormal than those in an ordinary dysplastic nevus.

Although it is not yet an invasive melanoma, it shares many microscopic features with melanoma in situ.

For this reason, many dermatologists and dermatopathologists manage severely dysplastic nevi in the same way as melanoma in situ, because distinguishing between the two can sometimes be difficult and because leaving abnormal cells behind may increase the risk of recurrence or progression.

Why Is Additional Surgery Needed?

Sometimes the biopsy removes only part of the lesion.

Or,

The abnormal cells extend right to the edge of the specimen (called a positive margin).

This means some abnormal cells may still remain in the skin.

Conservative Surgical Excision

To make sure all abnormal cells are removed, your dermatologist will recommend a conservative surgical excision.

This involves removing:

the biopsy scar
a small rim of normal-looking skin around it (called a surgical margin)

This greatly reduces the chance that abnormal cells remain.

Is This Surgery Urgent?

No.

This is not considered a medical emergency.

However,

it should not be ignored or postponed.

It is important to return for the recommended surgery within the timeframe advised by your dermatologist.

Does a Severely Dysplastic Nevus Mean I Have Melanoma?

Not necessarily.

Different pathologists may describe these lesions slightly differently.

Some experts consider severely dysplastic nevi to represent the very earliest stage along the spectrum toward melanoma, while others classify certain lesions as melanoma in situ when the microscopic changes meet stricter criteria.

Because of this overlap, many dermatologists follow melanoma in situ treatment principles and recommend complete excision with appropriate margins to ensure all atypical cells are removed.

The important point is that when the lesion is completely excised, the prognosis is excellent, and no additional treatment such as chemotherapy, radiation, or immunotherapy is required.

What Happens After the Surgery?

Once the lesion has been completely removed:

no additional treatment is usually necessary
no chemotherapy is needed
no radiation therapy is needed
no immunotherapy is needed

Your dermatologist or family doctor will simply monitor your skin during routine follow-up visits.

Will It Come Back?

If the lesion has been completely removed, recurrence is uncommon.

If abnormal cells are left behind, there is a greater chance the mole could recur at the biopsy site.

This is one reason why complete surgical excision is recommended for severely dysplastic nevi.

Am I at Higher Risk for Melanoma?

Yes—but this does not mean you will develop melanoma.

People with dysplastic nevi generally have a higher risk of developing melanoma somewhere on their skin compared with the general population.

This increased risk is related to the overall tendency of the skin to develop atypical moles, especially when combined with factors such as fair skin, significant sun exposure, or a family history of melanoma.

For this reason, lifelong skin surveillance is recommended.

    How Can I Reduce My Risk?

    Protect Your Skin From the Sun

    Use a broad-spectrum sunscreen (SPF 30 or higher) every day on exposed skin.
Reapply sunscreen every 2 hours when outdoors and after swimming or sweating.
Wear protective clothing, a wide-brimmed hat, and UV-blocking sunglasses.
Seek shade between 10 AM and 4 PM, when UV rays are strongest.
Avoid tanning beds completely.

Examine Your Skin Every Month

Become familiar with your own moles.

Look for:

new moles
changing moles
bleeding
itching
rapid growth
changes in color
irregular borders

If you notice any concerning changes, contact your dermatologist promptly.

Attend Your Dermatology Appointments

Your dermatologist will recommend follow-up visits based on:

the number of moles you have
your personal history
your family history
your level of sun damage
your biopsy results

Frequently Asked Questions

Did I do something wrong?

No.

Most dysplastic nevi develop because of a combination of genetics and accumulated sun exposure over many years.

Can sunscreen prevent new dysplastic nevi?

Sunscreen cannot completely prevent them, but regular sun protection significantly reduces ongoing UV damage and may lower the risk of developing additional atypical moles and skin cancers.

Will I develop melanoma?

Most people with dysplastic nevi never develop melanoma.

However, your risk is somewhat higher than average, which is why regular skin examinations and sun protection are important.

Can my children inherit this tendency?

Possibly.

Some families have a genetic tendency to develop atypical moles.

If several close relatives have numerous dysplastic nevi or melanoma, your dermatologist may recommend that family members also have periodic skin examinations.

Key Take-Home Messages

Dysplastic Nevus (Mild or Moderate)

Not melanoma.
Shows mild to moderate abnormal cells under the microscope.
If completely removed, treatment is complete.
No further surgery is usually needed.
Continue lifelong skin surveillance and sun protection.

Severely Dysplastic Nevus

Contains much more abnormal melanocytes and shares many microscopic features with melanoma in situ.
Often managed similarly to melanoma in situ because of this overlap.
If the biopsy margins are involved or close, complete surgical excision with a small margin of normal skin is recommended.
Once completely removed, the prognosis is excellent, and no additional cancer treatment is usually required.
Lifelong skin examinations and careful sun protection remain essential.

Disclaimer

This handout is intended to provide general education.

Individual treatment recommendations may vary depending on your pathology report, biopsy margins, medical history, and your dermatologist's clinical judgment.

Always follow the recommendations provided by your treating dermatologist.

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