A precursor lesion is one that existed before the melanoma, at the same site as the melanoma. A precursor is a non-malignant lesion that has the potential to become malignant. Lesions considered to be melanoma precursors include atypical (dysplastic) nevi, small or large congenital melanocytic nevi, lentigo maligna, atypical nevi on palms, soles and mucous membranes.

It is important to understand that the presence of a precursor lesion does not predict the future development of a melanoma at that site. Anyone with one or more precursor lesions should self-inspect regularly for any changes in size, shape or color, for elevation/nodule formation, or itchiness in the lesion. The lesion should be re-examined by a dermatologist every 6 to 12 months, or whenever changes are observed in the lesion.

The possibility of precursor lesions should be kept in mind during a skin self-examination. Precursor lesions may not fit the A-B-C-D criteria for recognizing suspicious lesions. Moreover, an early melanoma appearing as a new mole 3 millimeters in diameter and uniformly black in color does not fit the A-B-C-D criteria for diagnosis of melanoma.

Congenital Moles

A congenital mole is by definition a mole that is apparent at birth. Some moles that are presumed congenital based on large size may not be apparent at birth—e.g., tardive (late) congenital nevus. A congenital mole is classified by diameter as small if it can be excised easily and the wound closed primarily (without skin graft or tissue mobilization), while large is a term used to define lesions that may require a skin graft after removal. Giant congenital moles (also called "bathing trunk", "cape", or "garment") cover substantial portions of a major anatomic site. About 1 in 100 infants may be born with a congenital mole. Giant nevi occur 1 per 50,000 births.

Arbitrary size definition of small, medium and giant by diameter in millimeters does not take into account expansion of the nevus and growth of the anatomic site.

A giant congenital melanocytic nevus is shown in this photo:

Congenital moles are usually round or oval, flat or raised. They may be hairless or contain coarse hair. Color varies from light tan to dark brown. Typical changes over time include progressive darkening, progressive lightening, or irregular pattern of darkening. With giant congenital moles satellite lesions may occur on other anatomic sites.

Giant congenital moles range in color from light to dark to brown, may have satellite moles, and may contain coarse hair. The texture may be thick and leathery, or thin and soft. Changes within a giant mole may be difficult to detect because of the dark color and irregular surface of the mole.

All congenital moles are regarded as potential precursors for melanoma, and should be re-examined regularly. The statistical lifetime risk for malignant transformation of a congenital mole has been estimated at 5% to 40% in various studies, depending on size and anatomic site. A single deep nodule in a giant congenital mole may be the initial presentation of melanoma. In contrast, a surface color change is the most common presentation of melanoma in a small congenital mole.

Congenital moles that are present at birth should be evaluated regularly by an experienced dermatologist to determine if treatment is indicated. The decision to treat (surgically remove) a congenital mole may be made (1) to prevent the possibility of subsequent development of melanoma in the mole, and/or (2) for cosmetic reasons. There is risk for melanoma development in both large and small congenital moles. The risk is believed to be higher in very large congenital moles; after full medical evaluation and assessment of the infant’s ability to tolerate anesthesia and surgery, a very large congenital mole should be considered for removal after age 6 months. Not all physicians agree with the recommendation of attempted removal of giant congenital nevi early in life. If surgical removal is not possible—for example, the area of skin that must be removed is too large to be covered by a skin graft—arrangement must be made for regular re-examination of the mole by a dermatologist for the lifetime of the patient. Small congenital moles should be re-examined regularly for any indications of malignant transformation. Changes in color, shape or size of the congenital mole may be indications for immediate surgical removal. All small congenital moles are candidates for surgical removal before age 12 years, based upon their appearance, size and location, and the general health of the child. Not all physicians agree on the need or value of removing small congenital nevi.

A benign acquired mole is one that appears at any time during a lifetime but is not present at birth. Benign acquired moles are also called common moles. By age 3 years, 80% of children have at least one benign acquired mole; 90% of white adults and 70% of non-white adults have at least one. They may be dome-shaped, flat or polypoid (similar to a skin tag). Color ranges from skin tone to pink to brown; pigmentation may fade with age. A common acquired mole may enlarge as the body grows. Unlike atypical moles, the common mole tends to be small, have uniform pigmentation, and sharply defined edges.

Even though common acquired moles are benign, they are considered to have the potential for malignant transformation. Conditions that increase their risk for malignant transformation include:

the presence of 50 or more common acquired moles at least 2 millimeters in diameters on the face, body and/or extremities; and,

one of the moles changes in shape, size or color, or elevation or starts to bleed or itch.

Even when numerous and large, benign acquired moles are usually left untreated unless (1) biopsy is required for suspected malignant transformation, (2) a large mole is preventively removed from an area of the body that cannot be self-examined, (3) a mole is removed for cosmetic reasons, (4) in a dark-skinned person, a suspicious common mole on the palm of the hand, sole of the foot or under a toenail is believed to be a possible precursor to acral lentiginous melanoma. Fifteen percent of all persons have moles on palms or soles. Any black mole on palm, sole or nail should be evaluated, regardless of the ethnic derivation of the person or the size of the lesion.

Atypical moles are both precursor lesions and risk factors for melanoma (Click on Risk Factors Update. Dysplastic Nevi (Atypical Moles) as Risk Factors for Melanoma). The term clinically "atypical" is used to differentiate moles that do not conform to the "typical" criteria of symmetric shape, sharply defined borders, uniform color and contour, and size less than 5 millimeters in diameter. In contrast to "typical" moles, "atypical" moles are (1) not symmetric in shape, (2) do not have well defined borders, (3) are not uniform in color, (4) tend to be larger than 6 millimeters in diameter, and (5) are macular in appearance, with the center raised and the edge flat—i.e., appear as a discolored spot on the skin. Sometimes the atypical mole is described as having a "fried egg" appearance, with the center of the mole being darker in shade than the periphery. Sometimes the terms "atypical" and "dysplastic" are wrongfully used to mean the same thing. The term "dysplastic" is a histopathologic definition.

Atypical moles may change in appearance over time. Some become more "atypical", but they may also lose atypical features and gradually become more typical in appearance. Some may disappear. New atypical moles may appear at different sites—an event that is more likely in a person with a family history of atypical moles. About 5% of persons with atypical moles will develop a new or changed mole during a 12-month period; such lesions should be regarded as suspicious.

Numerous studies have shown that a person with atypical moles has a substantially increased risk for developing melanoma. The very presence of atypical moles is a marker for increased risk, while every atypical mole is a potential precursor of malignant transformation.

Atypical moles tend to "run in the family", and risk for developing melanoma may be associated with how many family members have had atypical moles and melanoma. According to a classification scheme cited in current medical literature, white-skinned persons with atypical moles and with or without a family history of atypical moles have a risk for melanoma 7-fold to 27-fold greater than that of the general white population. Persons with atypical moles and family history of melanoma in two or more family members have a risk for melanoma 148 times greater than that of the general white population. A person who has had melanoma and has one or more atypical nevi and comes from a family in which two or more members have had melanoma has a 500-fold risk for developing melanoma. The statistical analysis is based on the white-skinned population, which has a higher overall risk for melanoma than darker-skinned populations.

Because family history cannot always be known or verified, the current medical approach to patients who have atypical moles is to conduct periodic surveillance and remove lesions for biopsy at the earliest indication of possible malignant transformation.

Anyone with atypical moles, with or without a personal or family history of melanoma, should be under the care of a dermatologist, receiving regular full-skin examinations and follow-up monitoring.

Lentigo maligna (LM) is a lesion of older age. Persons older than age 60 are most at risk. Its development may be associated with cumulative damage to skin from solar radiation. In appearance, LM is usually a poorly defined, large, irregularly shaped, variably pigmented, totally flat area of skin. It occurs most frequently on the head and neck, especially the cheeks and nose. LM is considered to be a precursor lesion for lentigo maligna melanoma (LMM); studies have indicated that about 5% of LM undergoes malignant transformation to LMM. The definitive treatment for LM is surgical removal to prevent malignant transformation. Regular follow-up examination is essential because LM has a strong tendency to recur at the original site because of the difficulty in removing the lesion with adequate margins.

Skin self-examination for melanoma should be guided by the presence of new lesions, changing lesions, or an unusual mole, and awareness of the importance of precursors and markers as discussed a few paragraphs earlier. Two other criteria that may be helpful in skin self-examination are (1) the association between skin color and the most frequent sites for melanoma, and (2) in white-skinned people, the association between gender and the most frequent sites for melanoma.

African-Americans, sub-Sahara black Africans, Asians and other darker skinned populations experience an overall lower incidence of melanoma than white-skinned populations on a basis of incidence of cases per 100,000 population per year. The incidence of acral lentiginous melanoma is probably about equal among the various racial groups. The proportion of melanomas in dark-skinned peoples is dominated by melanomas on palms, soles, nail matrix and mucous membranes. Melanoma on palms, soles, nail matrix and mucous membranes comprises 2% of melanomas in whites, but 50% of melanomas in darker-skinned populations. Melanomas in dark-skinned groups, as in light-skinned groups, may occur on mucous membranes of the anus, nose, mouth, sinuses and genitals.

ALM occurs on parts of the body where other types of melanoma occur less frequently—on the soles of the feet, palms of the hands, under or at the edge of fingernails and toenails, and on mucous membranes of the nose, mouth and genitals.

These photos show ALM on characteristic locations of the body:

ALM on the toes.

ALM on the toes.

ALM on the foot.

While darker skinned people can have any type of melanoma at any site on the body, ALM occurs in this population with more frequency than any other type of melanoma.

In white-skinned people, melanoma occurs most frequently on the torso, head and neck, arms and legs, while about 2% occurs on palms, soles, nail matrix and mucous membranes.

In white-skinned populations, gender is associated with some statistical differences in the most frequent sites for melanoma. In white males, the most frequent sites are the skin of the back, chest and abdomen, upper arms, head and neck. In white females, the most frequent sites are the skin of the back, lower legs, upper arms, head and neck. The statistical differences are not great, except for an increase on the lower leg in women. As noted previously, melanoma can occur at any location on the skin or mucous membranes. It is important to remember that gender differences in melanoma are very slight—both males and females should self-examine all parts of the body where melanoma may occur. Also worth noting is that the most frequent sites for melanoma are often areas of the body that are difficult to self-examine—e.g., the back, buttocks, backs of the lower legs, mucous membranes of the mouth, nose and anus, and the hairy scalp. Especially in high-risk persons, members of the family should be enlisted in a regular routine of skin examination, especially of hard-to-examine areas, complemented by regular examinations by a dermatologist. Melanomas of the hairy scalp, genitalia and anal area are frequently discovered late because neither the patient nor members of the family examine these areas.

Family and personal medical histories are very important in helping a dermatologist assess a new patient’s risk for developing melanoma. Risk for melanoma is greatly increased when melanoma and/or atypical moles "occur in the family", or when the patient has had a previous melanoma. It is helpful when the patient can provide this type of family or personal medical history when seeing a physician for the first time.

Unfortunately, patients are sometimes not sure about definitions and details of medical histories. This may be especially true in differentiating between terms such as "carcinoma", "skin cancer", and "melanoma". A patient may recall that a parent or close relative had "skin cancer", but does not know whether it was basal cell carcinoma, squamous cell carcinoma, melanoma, or other type of malignant skin lesion. In a family history, a history of melanoma is a strong risk factor for melanoma, the deadliest form of skin cancer.

In some instances, patients themselves who had a previous skin cancer may not be sure whether it was melanoma.

A patient who has a personal medical history of cancer—of any type—should have that medical record transferred to the new dermatologist. The medical record should clarify questions about diagnosis and treatment of a previous skin cancer.

A patient who has a family history of skin cancer may have to rely on personal or family recollections if old medical records cannot be located. This makes risk assessment less specific. It is important for the dermatologist to know whether "skin cancer" in a personal or family medical history was melanoma. Risk assessment is part of overall awareness that can lead to earlier diagnosis and treatment of the deadliest form of skin cancer.

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