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Clinical Services at Rush Melanoma Risk Factors

Risk Factors for Developing Melanoma of the Skin

By Arthur R. Rhodes, MD, MPH

What is melanoma?

Melanoma of the skin is a potentially deadly cancer that develops as an unusual or “ugly” mole, a new mole on previously normal skin, or a preexisting mole that changes. Melanoma most often appears as a black or irregularly pigmented spot or bump, or occasionally a pink or red patch or growth. Melanoma is curable if detected and surgically removed in an early stage of development, before cancer cells have had a chance to spread to lymph nodes and vital internal organs via lymphatic and blood vessels in the skin.

Melanoma can occur anywhere on the skin or mucous membranes, in any racial group, and at any age, but this tumor occurs most commonly on the skin of white adults. Melanoma is extremely rare before age 12, and the incidence rate rises sharply after age 12. The life-time risk of developing melanoma is about l percent for whites. Melanoma is 1/15th to 1/20th as common in non-whites. When melanoma does occur in non-whites, about half the time it appears on palms, soles, nail beds, or mucous membranes (anus, genitalia, mouth, nose and conjunctivae).

What are the most important risk factors for developing melanoma?

The following melanoma risk factors are listed in decreasing order of importance:

  1. A new mole, or a mole that has changed or is changing
    The cells residing in the epidermis (most superficial layer of the skin) that produce the skin’s pigment (melanin) are called melanocytes. Moles are growths in the skin comprised of a cellular variant of melanocytes called nevomelanocytes. Another term for mole is nevomelanocytic nevus (plural, nevi). Nevi are usually acquired, and by the teen years, the average number of nevi per person is about a dozen. Approximately 90 percent of whites and 70 percent of non-whites have one or more nevi.

    People who have a new nevus, or a nevus that has changed or is changing, have a melanoma risk that is increased 20-fold to 100-fold compared to people who do not have this finding. A new nevus on previously normal skin, or a preexisting nevus that has changed in some way (color, borders, or surface), should be checked immediately by your doctor. Such a nevus may be melanoma or on its way to becoming melanoma. A change in a preexisting nevus could also represent infection, irritation, or some other type of lesion. Infection or irritation in a nevus will usually resolve within 7 to 10 days.

  2. Prominent mole pattern
    Melanoma risk can be assessed by measuring and counting nevi/moles. People who have at least 12 nevi ¼ inch in diameter (lentil bean size) or larger have a 41-fold increased melanoma risk. The presence of at least 5 nevi the size of a lentil bean or larger indicates a 7-fold increased melanoma risk, and at least 4 atypical nevi that size or larger a 29-fold increased risk. The presence of prominent numbers of smaller nevi also indicates an increased melanoma risk. The presence of at least 50 nevi at least as large as the long diameter of a sesame seed (1/16th inch) is associated with a 7-fold increased melanoma risk.

    Prominent numbers of relatively large moles often indicate the dysplastic nevus trait (see below). Among people who have an elevated melanoma risk because of prominent moles, melanoma can develop in a preexisting nevus or on previously normal skin. Prominent numbers of nevi and the presence of large nevi tends to occur as a familial trait. People who are affected with prominent nevi require periodic surveillance to detect the earliest signs that might indicate melanoma. Common benign growths that have no cancer risk and may be mistaken for nevi and even melanoma include seborrheic keratoses (brown or yellow-tan, dull patches comprised of benign epidermal overgrowth), cherry angiomas (small red bumps comprised of blood vessel overgrowth), warts, and skin tags.

  3. Dysplastic melanocytic nevi
    A dysplastic nevus is striking for relatively large size (lentil bean or larger), haphazard coloration or “fried egg” pattern, and often uneven or fuzzy borders. Abnormalities in dysplastic nevi fall midway between typical nevi and melanoma. Dysplastic nevi tend to occur as a familial trait, with an approximate 50 percent chance of passing the trait to offspring. New dysplastic nevi tend to appear throughout life. Dysplastic nevi usually occur by age 20 years among people destined to have them. The presence of one or more dysplastic nevi marks an individual as having at least a 7-fold increased melanoma risk. This risk is even higher if there are many dysplastic nevi and/or a personal or family history of melanoma.

    A dysplastic nevus may itself develop melanoma, or indicate a markedly increased risk at some other skin site. Melanoma may even develop in normal skin as a new mole in affected individuals. Only one dysplastic nevus is needed to develop melanoma.

    People who have any dysplastic nevi have an estimated 5 percent to 10 percent life-time risk of developing melanoma. The risk is less if high risk nevi are removed, but an increased melanoma risk persists. Approximately 40 percent of melanomas develop in a dysplastic nevus. Indications that melanoma may be developing in a dysplastic nevus include a change in color (usually a darkening, occasionally a lightening), development of a depigmented halo or total loss of pigment, and/or spreading of borders. Surface elevation, tenderness, itching, bleeding, and oozing tend to be more advanced signs.

  4. Congenital nevi
    A congenital nevus is a nevus that is present at birth. Most acquired nevi develop after the first 6 months of life. Only one percent of newborns have a congenital nevus. Congenital nevi are single in 95 percent of cases. Most congenital nevi are medium or light brown in color and distort the skin surface at least slightly. People who have a congenital nevus have an estimated 5 percent risk of developing melanoma by age 60 years. Approximately three percent to 15 percent of melanomas develop in a congenital nevus.

    Indications that melanoma may be developing in a congenital nevus include a rapid or slow change in color, surface, or border, usually in a portion of the nevus. In infants and children, congenital nevi usually expand in proportion to growth of the body part in which it is located. After body growth ceases, expansion of the nevus should cease. During infancy and childhood, congenital nevi tend to slowly change in pigmentation, hair, and surface characteristics. After body growth ceases, there should be no further change in size, color or surface characteristics in congenital nevi, and any such changes should be evaluated immediately by a physician.

  5. Lentigo maligna
    Lentigo maligna usually appears as a light brown “varnish stain” that is lentil bean size or larger on sun-damaged skin of whites, usually after age 35 years. People who have lentigo maligna have a 10-fold increased melanoma risk, and an estimated 5 percent life-time melanoma risk (within the spot). Lentigo maligna accounts for 5 percent of melanomas. Indications of melanoma developing in lentigo maligna include a darkening of color and/or spreading of borders, and later, surface elevation.
  6. Prior melanoma
    People who have had one melanoma of the skin have a 9-fold increased risk of developing another melanoma, compared to people who have never had melanoma. The increased melanoma risk is related to the presence elsewhere of high-risk nevi, including dysplastic nevi and congenital nevi. People who have had melanoma require lifelong periodic surveillance for new or changing nevi, the earliest signs that might indicate melanoma.
  7. Melanoma in a parent, sibling or child
    People who have a first degree blood relative with skin melanoma have an 8-fold increased melanoma risk and ought to be examined at least once yearly for early melanoma. The increased melanoma risk is believed to be related to the family trait of one or more high-risk nevi (including dysplastic nevi and congenital nevi) and/or a prominent nevus pattern. People who are affected with high risk nevi and prominent nevi require lifelong periodic surveillance for new or changing nevi, the earliest signs that might indicate melanoma.
  8. Immune system suppression
    Suppression of the immune system, which may occur because of disease or when medication is taken for an organ transplant or treatment for cancer, increases melanoma risk by 4-fold. People most at risk in this category include those who have prominent nevi and/or high-risk nevi, including dysplastic nevi and congenital nevi.
  9. Sun-induced freckles
    Dense sun-induced freckling increases melanoma risk by 3-fold. The presence of sun-induced freckling also indicates an increased risk for epithelial skin cancer (basal cell cancer and squamous cell cancer). Occasionally, a sun-induced freckle may transform to lentigo maligna (see above). 
  10. Sun sensitivity, relative inability to tan and excessive sun exposure
    People who are sun sensitive (tendency to sunburn) and have a relative inability to tan, have a two- to three-fold increased melanoma risk. Excessive sunlight exposure may also increase melanoma risk. The exact relation of sun sensitivity and excessive sunlight exposure to the development of melanoma is not as clear as that for epithelial skin cancer (basal cell cancer and squamous cell cancer). It is possible that excessive sunlight exposure or sun sensitivity brings out the tendency for nevi and freckles. It is also possible that excessive sunlight exposure may induce high-risk nevi and freckles to develop melanoma.

Everyone should practice sensible sun exposure habits to reduce premature skin aging and epithelial skin cancer, as well as to prevent melanoma. Sensible sun exposure means avoiding getting red in the sun, avoiding sun exposure during peak intensity (between 10 a.m. and 4 p.m. in most temperate climates from early spring to late fall), covering up with clothing if sun exposure is unavoidable, and using high SPF sunscreens to protect skin not easily covered by clothing. Sunscreens should not be relied on to prolong time spent in the sun. Sun protection during the first 15 years of life has been estimated to reduce the risk of epithelial skin cancer by 80 percent.

Epithelial skin cancer (basal cell cancer and squamous cell cancer) usually appears as an enlarging pink or warty bump or a non-healing sore and is most often related to excessive sun exposure and/or sun sensitivity and a family or personal history of epithelial skin cancer, or related to ionizing radiation (X-ray) therapy or scarring skin disease. Epithelial skin cancer is usually completely curable if recognized and treated in an early stage of development. Note that melanoma and epithelial skin cancer can occur in completely sun-protected areas of the skin, including palms of the hands, soles of the feet, nail beds, and mucous membranes.

Melanoma of the skin is curable if detected and surgically removed in an early phase of development. Do not ignore the warning signs of melanoma or high-risk traits.

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Melanoma Surveillance Clinic at Rush
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(312) 942-2195
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