Moles and cancer

ALSO KNOWN AS: Nevi (singular, nevus, or naevus)

RELATED CONDITIONS: Common acquired nevi (acquired in early decades of life), congenital nevi (acquired at birth), freckles, seborrheic keratoses, lentigos (age spots), dysplastic nevi, melanoma, basal cell carcinoma, squamous cell carcinoma

DEFINITION: Moles, or nevi, are clustered melanocytes or nevus cells that appear on the skin, usually brown. Melanocytes are cells in the skin that produce the pigment called melanin, which protects human skin from the damage of ultraviolet (UV) rays in sunlight.

Risk factors: Although almost everyone has moles, some factors may increase the risk of moles. People with lighter skin and with freckles have a slightly greater risk of developing melanoma. Exposure to ultraviolet rays from the sun can increase the number of moles, and the more moles a person has, the greater the risk of developing melanoma. Damage to the melanocyte deoxyribonucleic acid (DNA) can cause a mole to become cancerous. Lowered immune systems, such as those in persons with the human immunodeficiency virus (HIV) or who have had an organ transplant, can increase the development of moles.

Etiology and the disease process: Nevus cells (melanocytes) are normally localized in the basal layer of the skin (epidermis). A mole in itself is not dangerous and remains a stable part of the skin unless it becomes damaged and then can change into cancer.

Within sunlight are two types of invisible rays—infrared radiation (the sun’s heat) and ultraviolet radiation (ultraviolet light). Ultraviolet (UV) light is necessary for plants to live and generate energy. However, UV light can also cause sunburn, skin aging, and skin cancer under the right conditions. UV rays are further differentiated into UVA, UVB, and UVC. Studies are investigating UVA, once thought to be harmless, as a possible cause of skin cancer. Researchers believe that damaged melanocytes may reproduce in an uncontrolled and abnormal way, possibly causing melanoma, one dangerous form of skin cancer. The exact mechanisms by which skin cancer or malignant moles occur are still unclear.

Incidence: Most people have some form of moles, depending on their age, sun exposure, and genetic makeup. Usually, people have few moles as infants or children, but they may develop moles from puberty to age thirty. After that time, moles often disappear; therefore, older adults may have fewer moles. White adults have an average of twenty or fewer moles, but an average person can have ten to forty moles over a lifetime. Around 30 percent of melanoma cases begin in existing moles. With lifestyle changes and more exposure to sunlight, this number can increase.

The number of moles a person has is determined by genetics and exposure to sunlight. Moles are more common on parts of the body exposed to sunlight. Some evidence points to the role of the immune system in developing moles because they tend to develop in people with depressed immune systems, such as those infected with HIV and those who have had organ transplants.

Studies suggest that malignant nevi, such as melanoma, arise from preexisting moles. If this proves true, the more moles a person has, the higher the incidence of malignant nevi. The incidence of melanoma increased worldwide in the first decades of the twenty-first century.

Symptoms: Moles can be brown, pink, yellow, dark blue, or black and flat or raised. When a mole bleeds, itches, enlarges, turns multi-pigmented, or evolves with irregular edges, the patient should see a dermatologist, as this mole may need testing for cancer. Also, if moles are larger than six millimeters across, around the size of a pencil eraser, they should be checked by a physician.

Most moles are harmless, but people should monitor them for changes in color, size, texture, and the development of asymmetrical or irregular borders. A benign or noncancerous mole will remain stable in size, color, and shape for years. During pregnancy or puberty, moles may naturally change in color and size, becoming darker and larger.

Screening and diagnosis: Healthcare providers often check their patients’ moles during routine physicals or checkups. Patients should also check their moles periodically. The American Academy of Dermatology's "ABCDE" method helps individuals check moles for signs of melanoma. “A” stands for asymmetry and indicates that the halves of a single mole should be checked to see if they are different or asymmetrical; a normal mole has identical halves. “B” means to look at the borders or edges of the mole to see if they are irregular; usually, a noncancerous mole has regular distinct edges. “C” means that moles should be examined for color that varies within a single mole; ordinary moles are one color, not multipigmented. “D” is a reminder that the diameter of a malignant mole is usually larger than the size of a pencil eraser. "E" reminds patients to check for any moles that are evolving and to make note of any moles that are changing in size, shape, color, or elevation.

If changes appear in the mole, the patient should see a dermatologist who can provide more in-depth testing or removal of the mole. Some symptoms needing evaluation are bleeding, itching, crusting, or an unusual change. The eyes alone cannot diagnose a malignant mole. The dermatologist will biopsy or excise the mole for the pathologist to inspect. If the mole is malignant, the pathologist can provide a series of tests called staging. These tests may indicate whether the cancer has spread beyond the original site.

Treatment and therapy: Generally, nevi require no treatment unless they change into a cancerous mole. However, sometimes, they occur in an uncomfortable place and may be surgically removed. Failure to remove such a mole may result in bleeding from irritation. When a mole is found to be cancerous, it is surgically removed, along with some surrounding tissue.

Prognosis, prevention, and outcomes: Most moles are harmless. However, there are known risk factors that increase the incidence of moles, and some can cause adverse changes in their structure, leading to malignancies. People at high risk for melanoma should be vigilant for changes in their moles. About 99 percent of melanomas can be cured if caught in the early stages.

Although some exposure to sunlight is healthful because it supplies the body with vitamin D, intense exposure to UV rays, such as tanning, puts people at risk. UV rays cause more than 85 percent of melanomas. Sunburn experienced years earlier can still bring about changes in the skin that can precipitate a malignant mole. Young people often will not see the effects of overexposure to the sun’s rays until years later, so they may not feel motivated to change their behavior. People should use sun protection such as sunglasses, sunscreen, long-sleeved garments, and hats to decrease the risk of moles and the conversion of moles to cancer.

Bibliography

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Barnhill, Raymond L., Michael W. Piepkorn, and J. Klaus Busam. Pathology of Melanocytic Nevi and Malignant Melanoma. 3rd ed. Springer, 2014.

"Common Moles, Dysplastic Nevi, and Risk of Melanoma." National Cancer Institute, 17 Nov. 2022, www.cancer.gov/types/skin/moles-fact-sheet. Accessed 20 June 2024.

Massi, Guido, and Philip E. LeBoit. Histological Diagnosis of Nevi and Melanoma. 2nd ed. Springer, 2013.

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"Signs and Symptoms of Melanoma Skin Cancer." American Cancer Society, www.cancer.org/cancer/types/melanoma-skin-cancer/detection-diagnosis-staging/signs-and-symptoms.html. Acessed 20 June 2024.

Schofield, Jill R., and William A. Robinson. What You Really Need to Know About Moles and Melanoma. Johns Hopkins UP, 2000.

Waqar, Sara, et al. “Recognizing Histopathological Simulators of Melanoma to Avoid Misdiagnosis.” Cureus, vol. 14, no. 6, 20 Jun. 2022, doi:10.7759/cureus.26127.