Chapter 083. Cancer of the Skin (Part 1)

Harrisons Internal Medicine Chapter 83. Cancer of the SkinMelanoma Pigmented lesions are among the most common findings on skin examination. The challenge is to distinguish cutaneous melanomas, which may be lethal, from the remainder, which with rare exceptions are benign. Examples of malignant and benign pigmented lesions are shown in Fig. 83-1.Figure 83-1Atypical and malignant pigmented lesions. The most common melanoma is superficial spreading melanoma (not pictured). A. Acral lentiginous melanoma is the most common melanoma in blacks, Asians, and Hispanics and occurs as an enlarging hyperpigmented macule or plaque on the palms and soles. Lateralpigment diffusion is...
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Chapter 083. Cancer of the Skin (Part 1) Chapter 083. Cancer of the Skin (Part 1) Harrisons Internal Medicine > Chapter 83. Cancer of the Skin Melanoma Pigmented lesions are among the most common findings on skinexamination. The challenge is to distinguish cutaneous melanomas, which may belethal, from the remainder, which with rare exceptions are benign. Examples ofmalignant and benign pigmented lesions are shown in Fig. 83-1. Figure 83-1 Atypical and malignant pigmented lesions. The most common melanomais superficial spreading melanoma (not pictured). A. Acral lentiginous melanomais the most common melanoma in blacks, Asians, and Hispanics and occurs as anenlarging hyperpigmented macule or plaque on the palms and soles. Lateralpigment diffusion is present. B. Nodular melanoma most commonly manifestsitself as a rapidly growing, often ulcerated or crusted black nodule. C. Lentigomaligna melanoma occurs on sun-exposed skin as a large, hyperpigmented maculeor plaque with irregular borders and variable pigmentation. D. Dysplastic nevi areirregularly pigmented and shaped nevomelanocytic lesions which may beassociated with familial melanoma. Epidemiology Melanomas originate from neural crest-derived melanocytes; pigment cellspresent normally in the epidermis and sometimes in the dermis. This tumor affectsaround 62,000 individuals per year in the United States, resulting in 7910 deaths.Melanoma is the fifth most common cancer in men (5% of cancers) and the sixthmost common in women (4% of cancers). The tumor can affect adults of all ages,even young individuals (starting in the mid-teens); has distinct clinical featuresthat make it detectable at a time when cure by surgical excision is possible; and islocated on the skin surface, where it is visible. The incidence has increaseddramatically (6% per year from 1973 to 1980, then 3% per year). Current lifetimerisk ratio is 1:53 in males and 1:78 in females. The reason for this increase isuncertain but may involve increased recreational sun exposure, especially early inlife. Individuals of similar ethnic background who immigrate after childhood toareas of high sun exposure (e.g., Israel and Australia) have lower melanoma ratesthan individuals of similar age who were either born in those countries orimmigrated before age 10. The individuals most susceptible to development ofmelanoma are those with fair complexions, red or blond hair, blue eyes, andfreckles and who tan poorly and sunburn easily. Other factors associated withincreased risk include a family history of melanoma (~1 in 10 melanoma patientshave a family member with melanoma), the presence of a clinically atypical mole(dysplastic nevus) or a giant congenital melanocytic nevus, the presence of ahigher than average number of ordinary melanocytic nevi, andimmunosuppression (Table 83-1). Individuals with 50 or more moles ≥2 mm insize have a 64-fold increased risk. About 30% of melanomas arise in a nevus.Some individuals with multiple primary melanomas and/or a strong family historyhave heritable mutations in the CDKN2A gene. Melanoma is relatively rare inheavily pigmented peoples. Dark-skinned populations (such as those of India andPuerto Rico), blacks, and East Asians have rates 10–20 times lower than lighter-skinned whites. In keeping with the role of sun exposure, the incidence isinversely correlated with the latitude of residence; at any latitude, darker-skinnedpersons have the lowest incidence. Melanoma is rare in children under age 10. Table 83-1 Risk Factors for Cutaneous Melanoma High risk (>50-fold increase in risk) Persistently changing mole Clinically atypical moles in patient with two family members withmelanoma Adulthood (vs. childhood) >50 nevi ≥2 mm in diameter Intermediate risk (~10-fold increase in risk) Family history of melanoma Sporadic clinically atypical moles Congenital nevi (?) White ethnicity (vs. black or East Asian ethnicity) Personal history of prior melanoma Low risk (2- to 4-fold increase in risk) Immunosuppression Sun sensitivity or excess exposure to sunSource: Adapted from AR Rhodes et al: JAMA 258:3146, 1987.