Some dysplastic nevi look extremely similar to melanoma and a biopsy may be needed to tell them apart.

Dysplastic nevi (singular: nevus), also called Clark’s nevi, are atypical moles that look different than common moles. They tend to have:

  • irregular borders
  • a mix of color
  • larger size

Melanoma is the deadliest type of skin cancer. It usually has a good outlook when caught early, but it’s difficult to treat if diagnosis is delayed.

Let’s look at the similarities and differences between these two skin conditions.

Dysplastic nevus with moderate atypia

Dysplastic nevi are divided into mild, moderate, and severe depending on their features identified on a biopsy. The difference between these three grades is largely subjective, but moderate atypical nevi tend to be larger than mild nevi with variation in their color and irregular edges.

Dysplastic nevus with severe atypia

Severe dysplastic nevi are indistinguishable from early melanoma. They show considerable irregularity of their edges and irregular color. They should be surgically removed.

Severe dysplastic nevi and melanoma may be indistinguishable without a biopsy.

Dysplastic nevus symptoms

Compared to common moles, dysplastic nevi may:

  • be larger
  • be flat with some raised parts
  • have smooth, scaly, or rough patches
  • have an irregular border or a faded border
  • be multicolored

Melanoma symptoms

A new mole or a change in one of your previous moles can be signs of melanoma. Some cases of melanoma develop from previous dysplastic nevi, but this isn’t common.

Melanoma’s typical appearance is characterized by the acronym ABCDE:

  • A: asymmetry
  • B: irregular or poorly defined borders
  • C: varying colors
  • D: a diameter larger than a pencil eraser
  • E: evolving in size, shape, or color

Melanoma most often appears in areas exposed to sunlight.

Here’s a look at the causes and risk factors for melanoma and dysplastic nevi.

Dysplastic nevus causes and risk factors

The cause of a dysplastic nevi often isn’t known, but the risk factors include:

  • lighter skin
  • skin that’s sensitive to the sun
  • light-colored hair
  • light-colored eyes
  • skin that’s prone to freckling

Melanoma causes and risk factors

The cause of melanoma often isn’t known, but it’s associated with ultraviolet light exposure from sunlight or indoor tanning equipment.

Risk factors for melanoma include:

  • having many moles
  • having many atypical moles
  • having dysplastic nevus syndrome, where you have many dysplastic nevi
  • family history of melanoma
  • personal history of melanoma or other skin cancer
  • having a weak immune system
  • older age
  • male sex
  • xeroderma pigmentosum

Severe dysplastic nevi have the potential to turn into melanoma. It’s rare for this to happen, but the risk increases the more atypical moles you have.

The odds of developing melanoma are about 10 times higher for somebody with five dysplastic nevi than somebody who has none.

It’s important to see a doctor if you notice a new or changing spot on your skin, especially if it has any of the ABCDE signs of melanoma, like multiple colors or poorly defined borders.

Learn more about these signs here.

A dermatologist can spot a dysplastic nevus during a physical exam, but they may only be able to differentiate it from melanoma by taking a biopsy, which allows the cells to be examined under a microscope in a laboratory.

They can also use the results of a biopsy to grade dysplastic nevi from mild to severe.

Here’s how dysplastic nevi and melanoma are treated.

Dysplastic nevus treatment

A dysplastic nevus may not need treatment unless your biopsy shows cancerous changes and it’s moderate or severe. Treatment usually involves removing the mole and a small border of healthy tissue around it.

You may also receive Mohs surgery. During this procedure, a thin layer of cells is shaved off your mole and they’re checked for cancer. Your surgeon will continue to shave layers until there are no more abnormal cells.

Melanoma treatment

The most common treatment for melanoma involves surgery to remove the mole and possibly nearby lymph nodes. You may also receive radiation therapy.

Advanced cancers may need:

Atypical moles largely aren’t preventable. It’s a good idea to protect your skin if you have atypical moles to prevent them from transforming into melanoma.

Ways to prevent melanoma include:

  • staying out of direct sunlight as much as possible
  • covering up with long sleeves when you’re out
  • using sunscreen with SPF 15 or higher
  • avoiding use if indoor tanning machines
  • checking your skin regularly for changes

Here are some frequently asked questions people have about dysplastic nevi and melanoma.

Is a severe dysplastic nevus cancer?

Dysplastic nevi aren’t cancer, but some have the potential to become cancer.

Should dysplastic nevi be biopsied?

Dysplastic nevi are commonly biopsied to check for melanoma. Severe dysplastic nevi can be indistinguishable from early melanoma and should be removed.

What percentage of dysplastic nevi become melanoma?

Most dysplastic nevi never become melanoma.

About 30% of dysplastic nevi associated with BRAFor NRASmutations are at risk of cancerous transformation. The lifetime risk of melanoma in the United States is less than 1% but it increases to more than 10% in people with atypical nevi.

Dysplastic nevi can resemble melanoma and may require a biopsy to differentiate them. Some dysplastic nevi can transform into melanoma.

It’s important to see a doctor if you notice a new spot on your skin. It’s particularly important if the spot changes size, shape, or color.