Not all moles turn into melanoma, and not all melanomas develop from a mole.

By Madison Yauger
June 08, 2021

Birthmark, beauty spot, mole-whatever you call them, these little growths tend to pop up throughout our lives. For the most part, these moles are harmless, serving only as markers to signal our uniqueness. But sometimes moles can be-or turn-cancerous, and potentially even deadly.

cancerous moles , Dermatologist examining moles of patient
Credit: Adobe Stock

Technically speaking, a cancerous mole is known as a melanoma, or a type of " (ACS), an estimated 106,110 cases of melanoma will be diagnosed this year, and 7,180 people are likely to die from this aggressive form of skin cancer.

As you may already know, the biggest contributor to melanoma-as with most types of skin cancer-is repeated, unprotected exposure to ultraviolet (UV) rays, not only from the sun but also artificial sources like tanning beds. But there's still a lot about cancerous moles you may not be aware of, like symptoms and treatment options. Here's what you need to know.

What is a cancerous mole?

First things first: A mole-technically known as a nevus, or nevi for multiple moles-is a common growth that develops on your skin, either dating back to childhood, or later in life, according to the American Academy of Dermatology Association (AADA). These growths happen when your pigment cells, or melanocytes, grow in clusters creating an overgrowth on the skin, the National Cancer Institute (NCI) says. Some moles may appear flat or raised, dark or light, and if you have lighter skin you could have anywhere between 10 and 40 moles on your body.

It's important to remember that not all moles are or will turn cancerous. "When we talk about moles there are congenital moles-like birth marks-moles that are completely benign, and then there are [dysplastic] moles with some atypic, meaning under the microscope we see atypical or odd-looking cells," Mary L. Stevenson, MD, a dermatologic surgeon based in New York City, tells Health.

Congenital moles are usually small, have a round smooth surface, and are dome-shaped, according to the NCI. They're also usually pink or brown, with the color generally coordinating to your complexion tones-lighter moles on those with fair skin and hair color, and darker moles on those people with darker skin and hair. Dysplastic nevi, or atypical moles, may be larger than common moles, with different characteristics in shape, color, and texture, according to the NCI. Many atypical moles are flat instead of round, and have an irregular border.

Both of those moles have the potential to become cancerous-but the chances of that happening are very slim. Dysplastic nevi specifically have a slightly higher chance of becoming cancerous, since the they already contain some atypical cells (keeping an eye out for changes is important here, but more on that later). It's important to note that a cancerous mole can pop up on areas of the skin that were previously clear or free of moles, as well.

A cancerous mole is known as a melanoma, or a malignant melanoma, Debra Jaliman, MD, a board-certified dermatologist and assistant clinical professor of dermatology at the Icahn School of Medicine at Mount Sinai, tells Health. In addition to developing from a common mole, an atypical mole, or just a clear spot of skin, melanoma can also show up in the eye, digestive system, or in other areas of the body, per the NCI.

Remember: Melanoma is the deadliest type of skin cancer. That's because, as opposed to other common types of skin cancers, melanoma can invade nearby tissue and spread to other areas of the body (aka metastasize) like the lungs, liver, bone, or brain, the NCI says.

What causes a mole to become cancerous?

Obviously, not every mole will turn into a melanoma, and not every melanoma stems from a strange mole, says Dr. Jaliman. In fact, researchers don't know exactly what causes some moles to turn cancerous, while others stay benign, though there are a handful of risk factors that contribute.

Sunlight or artificial rays from tanning beds or other sources are one major risk factor. "UV [ultraviolet] light exposure is the single biggest risk factor for the development of cancerous spots," Joshua Zeichner, MD, associate director of cosmetic and clinical research in dermatology at Mount Sinai Hospital, tells Health. "The UV light causes free radical damage to the skin cells and leads to a transformation into an atypical, unregulated cell."

Having a large amount of moles-more than 50 common moles, or more than five atypical moles-can also up someone's risk of developing melanoma, per the NCI.

Other risk factors include: having fair skin, freckling, and light hair; a family or personal history of skin cancer or melanoma, and having a weakened immunes system, either from illness or medication. Being older and male are also risk factors for melanoma, the NCI says.

What are the symptoms of a cancerous mole?

For the most part, both common and atypical moles should stay the same, regarding size, shape, and color-and it's when any mole, old or new, begins to change, that you should take notice.

There are a few different ways to examine moles to see if they're concerning. The first is called the ABCDE method, says Dr. Zeichner, who describes the acronym below:

  • A: Asymmetry, when one side does not look like the other side.
  • B: Border, when the border is jagged or punched out rather than smooth.
  • C: Color, when a mole has multiple colors to it, like brown, black, white, or blue.
  • D: Diameter, when a mole has a diameter greater than six millimeters (aka the size of a pencil eraser).
  • E: Evolution, when a mole changes in shape or appearance over time.

Another common symptom of cancerous moles is discomfort like itchiness or pain, according to the AADA.

Seeing brand-new moles pop up on your skin-also known as acquired moles-may also be something to watch out for. Though common, these moles lead to melanoma more often than congenital moles. According to The Skin Care Foundation, only 20%-30% of melanomas are found in existing moles-the other 70%-80% arise in "normal-looking" skin. So, if you have a new mole that looks concerning, you should get it checked out.

How are cancerous moles treated?

If you or your doctor discovers a concerning mole, it will normally be placed into one of three categories: mild, moderate, and severely atypical (meaning you should get it checked immediately), says Dr. Stevenson. "Generally speaking we remove atypical moles that are moderate or severe to ensure [the] entire lesion is out and there was not a sampling error with the biopsy that only took a portion of the specimens," she says.

If a skin biopsy determines melanoma, swift action is necessary, since the type of skin cancer can spread very quickly to other tissues and organs, per the AADA. Depending on the stage of your cancer, along with other factors, your care team will come up with a treatment plan for the melanoma, that may contain any of the following options.

Surgery

According to the ACS, surgery is the main treatment option for most melanomas, and it is usually able to cure early stages of the disease. The types of surgery include: wide excision, Mohs surgery, lymph node dissection, metastatic melanoma surgery, and extremely rare cases, amputation.

Wide excisions are used when thin melanoma (superficial layers of skin) is diagnosed by a skin biopsy, and involves removing the tumor and a small area of healthy skin around the area to ensure removal of all cancerous cells. Mohs surgery involves a specialist removing thin layers of skin one section at a time until no cancer cells are detected, and leaves less of a scar. In rare situations, amputation may be considered if the melanoma is deep in a digit like a finger or toe. A lymph node dissection removes the lymph nodes around the melanoma tumor where it would most likely spread first. Finally, if the melanoma has spread, then metastatic melanoma surgery could be an option, but it would be to control the cancer, not cure it.

Therapies

Once the melanoma becomes more aggressive, other types of therapy may be considered, like immunotherapy, targeted therapy, chemotherapy, and radiation therapy, according to the ACS.

Immunotherapy uses medication to kick-start your immune system, with the hope that it will destroy cancer cells more effectively. Targeted therapy also uses medication, but instead of boosting on your immune system to work on a higher level, these drugs track down the cancer cells themselves to try to destroy them. A third option is chemotherapy which also works to kill cancer cells by sending medication through the bloodstream. Radiation therapy can also be considered, and uses high beams of rays to destroy the cancer cells. Before considering any of these approaches, you should consult your doctor to determine the best form of treatment.

How can you prevent cancerous moles?

Prevention is key when it comes to protecting yourself against melanoma and other types of skin cancer. And while some risk factors can't be controlled-like your age, sex, or family history-there are some things you can do to help lower your overall risk.

First and foremost, you want to limit your exposure to UV rays as much as possible-that means practicing sun safety while you're outside and not exposing yourself unnecessarily (like in a tanning bed). When you do go outside, protect your skin through sunscreen, as well as protective clothing, a hat, and sunglasses.

Keeping track of how your skin looks is important too. "If you notice a new or changing spot, make sure to get it checked by your dermatologist ASAP," says Dr. Zeichner. "When detected early the atypical moles can be removed completely without any risk of progression into skin cancer." Keeping an eye on your skin in general is a good idea too-not just if you detect changes. Dr. Stevenson recommends everyone get checked twice a year by a dermatologist-especially if you have any of the risk factors of skin cancer.

To get our top stories delivered to your inbox, sign up for the Healthy Living newsletter