Porth's Essentials of Pathophysiology, 4e

1174

Integumentary Function

U N I T 1 3

malignant melanoma over the past several decades has been credited to increased UV light exposure, includ- ing tanning salons. Other risk factors include a family history of malignant melanoma, fair hair and skin, ten- dency to freckle, and a history of blistering sunburns as a child. Still other significant risk factors for melanoma are atypical moles/dysplastic nevus syndrome, immuno- suppression, and prior PUVA therapy. Roughly 90% of malignant melanomas in whites occur on sun-exposed skin. However, in darker-skinned people melanomas often occur on non–sun-exposed areas, such as the mucous membranes and subungual, palmar, and plantar surfaces. Malignant melanomas dif- fer in size and shape. Usually, they are slightly raised and black or brown. Borders are irregular and surfaces are uneven. Most appear to arise from preexisting nevi or new molelike growths (Fig. 46-22). There may be surrounding erythema, inflammation, and tenderness. Periodically, melanomas ulcerate and bleed. Dark mela- nomas are often mottled with shades of red, blue, and white. These three colors represent three concurrent processes: melanoma growth (blue), inflammation and the body’s attempt to localize and destroy the tumor (red), and scar tissue formation (white).

Skin Cancer Skin cancer represents the most common malignancy in white-skinned people in the Western world. 61 The majority of skin cancers are nonmelanomas, either basal cell or squamous cell carcinoma, which are not associated with a high risk of morbidity or mortality. Although malignant melanoma represents a small subset of skin cancers, it is the most deadly. In 2009 61,646 people in the United States were diagnosed with malig- nant melanoma—35,436 men and 26,210 women. 61 In the United States, 9199 people also died from melano- mas of the skin (5992 men and 3207 women). 61 The rising incidence of melanoma and other skin cancers has been attributed to increased sun exposure associated with social and lifestyle changes. 62 The factors linking sun exposure to skin cancer are not completely understood, but both total cumulative exposure and altered patterns of exposure are strongly implicated. Basal cell and squamous cell carcinomas are often associated with total cumulative exposure to UV radiation. Thus, basal cell and squamous cell carcinomas occur more commonly on maximally sun-exposed parts of the body, such as the face and back of the hands and forearms. Melanomas occur most commonly on areas of the body that are exposed to the sun intermittently, such as the back in men and the lower legs in women. 62 They are more common in persons with indoor occu- pations whose exposure to sun is limited to weekends and vacations. Excessive childhood sun exposure is an important risk factor for melanoma, particularly blister- ing sunburns. 63 Malignant Melanoma Malignant melanoma is a cancerous tumor of the mela- nocytes. 64,65 It is a rapidly progressing, metastatic form of cancer. The dramatic increase in the incidence of FIGURE 46-21. Dysplastic nevi. Lesion has a dark brown “pebbly” elevated surface against a lighter tan, macular background.The irregular, indistinct margin helps to distinguish it from the small congenital pattern nevus, which some dysplastic nevi closely resemble. Its distinct morphology, rather than its size (6 × 6 mm), identifies it as a dysplastic nevus (From National Cancer Institute Visuals. No. AV-8500-3696.)

FIGURE 46-22. Melanoma lesions, demonstrating the ABCD rule: A (asymmetry), B (irregular borders), C (different colors), and D (diameter change in size). (From National Cancer Institute Visuals. Nos. AV-8809-4036, AV-8809-4037. Courtesy of Skin Cancer Foundation.)