What are moles? How can moles become cancerous?

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 in color. Melanocytes are
cells in the skin that produce the pigment called melanin that
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 development of
moles.

Etiology and the disease process: Nevus cells (melanocytes) are normally localized in the basal layer of the skin (epidermis). A mole of 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, aging of the skin, and, under the right conditions,
skin
cancer. 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
is 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 an infant
or child but may develop moles from puberty to the age of thirty. Often after that
time, moles begin to disappear so that 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, with a risk of 1:100 turning into a malignant
melanoma. 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 that are exposed to sunlight. Some evidence points to a role by the immune system in developing moles because they tend to develop in people with depressed immune systems such 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 has been increasing worldwide.
Australia has the highest incidence of melanoma.

Symptoms: Moles come in various colors and shapes. Some are brown and others are pink. Some are yellow, dark blue, or black. Moles can be flat or raised.

Most moles are harmless but people should monitor their moles for changes in
color, size, and texture, and for 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.

When a mole bleeds, itches, enlarges, turns multipigmented, or evolves with irregular edges, the patient should see a dermatologist, as this mole may need testing for cancer.

Screening and diagnosis: Health care providers can check their
patients’ moles during routine physicals or checkups. Also, people can check their
own moles periodically. One way to check moles for signs of melanoma is called the
ABCDEs of melanomas. “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 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 that may need
evaluation are bleeding, itching, crusting, or an unusual change. The eyes alone
cannot diagnosis 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, the mole, along with some surrounding tissue, is surgically removed.

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 the structure of the moles, leading to
malignancies. People at high risk for melanoma should be vigilant for changes in
their moles.

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.
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. To decrease the risk of moles as well as the conversion
of moles to cancer, people should use sun protection such as sunglasses,
sunscreen, long-sleeved garments, and hats.

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

Hearing, Vincent
J., and Stanley P. L. Leong, eds. From Melanocytes to Melanoma: The
Progression to Malignancy. Totowa: Humana, 2006.
Print.

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

Niederhuber, John E., et al.
Abeloff's Clinical Oncology. 5th ed. Philadelphia:
Elsevier, 2014. Print.

Poole, Catherine
M., and Dupont Guerry IV. Melanoma: Prevention, Detection, and
Treatment. 2nd ed. New Haven: Yale UP, 2005. Print.

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