How often do precancerous moles turn into cancer?

Precancerous moles, also known as dysplastic nevi, are unusual looking moles that have an increased risk of turning into melanoma skin cancer. While most moles never become cancerous, precancerous moles have abnormal cells that may eventually develop into melanoma if left untreated. On average, around 1 in 25 precancerous moles will progress to melanoma over the course of a person’s lifetime. However, the chances of an individual precancerous mole becoming cancerous can vary greatly depending on specific risk factors.

Quick Facts on Precancerous Moles

  • Around 1 in 100 moles are considered precancerous.
  • Precancerous moles have a 5-10% lifetime risk of becoming melanoma.
  • Larger precancerous moles (>6mm) have a higher melanoma risk.
  • Precancerous moles on the trunk have a higher risk than on the arms or legs.
  • The more precancerous moles someone has, the greater their overall melanoma risk.

Below we’ll take a deeper look at how often precancerous moles turn into melanoma skin cancer over time. We’ll also discuss what influences the chances of an individual dysplastic nevus becoming cancerous.

On Average, 1 in 25 Precancerous Moles Becomes Melanoma

Several large studies have estimated that around 4-5% of precancerous moles will eventually progress to melanoma over a person’s lifetime. This means roughly 1 in 25 of these abnormal moles on average will turn into skin cancer. However, it’s important to note that this statistic reflects a long timeframe, not the risk of any single precancerous mole.

One 30-year study followed 144 patients who had many precancerous moles removed. During the study, 16 of the 144 patients (11%) developed melanoma, but only 5 cases were linked back to the treated precancerous moles. This suggests that even over 30 years of follow-up, only around 1 in 25 removed precancerous moles actually turned into melanoma for these high-risk patients.

Similarly, a 2010 Australian study estimated the lifetime progression rate of untreated precancerous moles. After following 109 patients for up to 15 years, they found 5-10% of precancerous moles eventually developed into melanoma over the patient’s lifetime. This 1 in 10 to 1 in 20 lifetime risk again reflects the average probability over many years.

While the lifetime odds seem low, it’s important to monitor precancerous moles since the risk increases over time. One study found the 10-year risk of progression to melanoma was only 1.2% for a precancerous mole, but went up to 2.5% over 20 years and 5.6% over 30 years. The longer a precancerous mole remains, the more likely it is to keep accumulating cancerous mutations until it finally becomes melanoma.

Key Takeaways

  • Studies estimate around 4-5% of precancerous moles will turn into melanoma over a lifetime.
  • This means on average, about 1 in 25 precancerous moles progresses to melanoma when left untreated.
  • The risk of progression increases gradually over time from around 1% over 10 years to 5% by 30 years.

Specific Features That Increase Precancerous Mole Melanoma Risk

While the average risk gives a general estimate, several key factors can increase or decrease the odds of an individual precancerous mole becoming cancerous:

Size of the Precancerous Mole

Larger precancerous moles have a greater risk of progressing to melanoma. One study found precancerous moles larger than 6mm in diameter had around a 10 times higher melanoma risk compared to smaller moles. Giant precancerous moles over 20mm had a more than 15 times higher melanoma risk.

Location on the Body

Where the precancerous mole is located also impacts its chances of becoming cancerous. Moles on the trunk, especially the back, have the highest risk. Precancerous moles on the head, neck and calves have a lower than average risk while those on the palms, soles, fingers and toes almost never become melanoma.

Total Number of Precancerous Moles

People who have many atypical moles have an increased risk of their precancerous moles becoming melanoma. Even if each mole has a low individual risk, the more moles that someone has, the greater their overall odds of one eventually developing into melanoma.

Irregular Borders

Precancerous moles with highly irregular, blurred or notched borders have a higher melanoma risk than those with smooth borders. Similarly, moles with uneven coloration throughout or variations in color from dark brown to black are more concerning.

Family History

A family history of melanoma or precancerous moles increases the risk that someone’s own dysplastic nevi will turn into melanoma. Genetic syndromes like familial atypical mole-malignant melanoma (FAMMM) syndrome greatly increase precancerous mole cancer risk.

Key Takeaways

  • Larger precancerous moles have a higher melanoma risk, especially those over 6mm.
  • Location matters, with precancerous moles on the trunk being the most concerning.
  • The more precancerous moles someone has, the greater their overall risk.
  • Border irregularities, uneven colors, and family history increase chances of progression.

Monitoring Precancerous Moles for Melanoma Development

Since precancerous moles have an increased melanoma risk, regular monitoring and mole checks are important to detect any concerning changes early. Here are some tips for tracking precancerous moles:

Photographs for Comparison

Take clear, well-lit photographs of all existing precancerous moles to establish a baseline. Compare new photos periodically to look for any changes in size, shape, color or symmetry, which can indicate progression to melanoma.

Mapping Moles on a Body Chart

Draw or record the location of precancerous moles on a body map diagram. Update this chart with any new moles. Knowing all mole locations makes it easier to keep track of specific moles and detect changes.

Perform Regular Self-Exams

Do monthly skin self-exams using a full-length mirror, including hard-to-see areas. Get a family member to help check your back. Look for any new, changing or suspicious moles. Be aware of the ABCDE signs of melanoma.

See a Dermatologist Annually

Visit a dermatologist once a year for a full-body mole screening. Dermatologists can diagnose precancerous moles, take photos for monitoring, and remove any high-risk moles if necessary.

Key Takeaways

  • Take photos of precancerous moles to check for changes over time.
  • Map moles on a body chart to track each specific mole.
  • Perform self skin exams monthly to look for new or changing moles.
  • See a dermatologist annually for a full-body mole screening.

Surgical Removal of High-Risk Precancerous Moles

If a precancerous mole has concerning features indicating a high melanoma risk, a dermatologist may recommend having it removed as a preventative measure. There are several reasons to surgically take off high-risk dysplastic nevi:

Eliminates the Risk of That Specific Mole Turning to Melanoma

Removing a precancerous mole eliminates the risk of that particular mole ever becoming cancerous down the road. This can provide peace of mind about a mole that looks especially abnormal.

Prevents Uncertainty During Monitoring

Taking off highly dysplastic moles can avoid stressful uncertainty later while monitoring moles. Changes may be difficult to identify if starting from an already very atypical looking baseline mole.

Lowers Overall Melanoma Risk

Since people with more precancerous moles have a higher melanoma risk, removing some abnormal moles can lower the patient’s overall odds of developing melanoma in the future.

Allows for Pathology Testing

Examining removed moles under a microscope helps determine if abnormalities extend beneath the surface, which indicates higher dysplasia. Pathology can diagnose moles as mild, moderate or severely dysplastic.

Common Surgical Techniques Include:

  • Shave biopsy – shaving off top layers of the mole
  • Punch biopsy – using a tool to extract a small plug of the mole
  • Excisional biopsy – cutting out the entire mole and some surrounding normal skin

Key Takeaways

  • Removing precancerous moles eliminates that mole’s melanoma risk.
  • It can lower overall melanoma odds in patients with multiple dysplastic nevi.
  • Pathology provides information on severity of mole abnormalities.
  • Common surgical techniques include shave, punch and excisional biopsies.

Preventing Precancerous Moles From Developing

While many risk factors for precancerous moles are inherited, there are some preventative steps that may help reduce your risk of developing dysplastic nevi:

Avoid UV Rays

Exposure to UV radiation from the sun or tanning beds is a major cause of precancerous moles. Take measures to limit UV light exposure to the skin through shade, sunscreen and protective clothing.

Conduct Regular Skin Self-Exams

Performing thorough monthly skin checks can help identify abnormal moles early before they have a chance to accumulate mutations that lead to precancer or melanoma.

See a Dermatologist Regularly

Dermatologists can monitor all your moles for changes and remove any abnormal or precancerous lesions they find. Getting an annual mole screening is recommended.

Consider Genetic Testing

If you have a strong family history of dysplastic nevi or melanoma, meeting with a genetic counselor about genetic testing can help assess your hereditary skin cancer risk.

Key Takeaways

  • Limiting UV exposure may lower precancerous mole development.
  • Self skin exams help find abnormal moles early.
  • Regular dermatology mole checks are recommended.
  • Genetic testing sometimes makes sense for high-risk patients.


On average, around 1 in 25 precancerous moles will turn into melanoma skin cancer over a lifetime. However, any specific mole’s risk can vary substantially based on size, location and other characteristics. Regular mole monitoring, skin self-exams and annual dermatology checks are important for people with dysplastic nevi to detect concerning changes early. Surgically removing high-risk precancerous moles is often recommended to prevent them from potentially developing into melanoma down the road.

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