General Considerations
Classification
Tumors of the cutaneous surface may arise from the epidermis, dermis, or subcutaneous tissue or from any of the specialized cell types in the skin or its appendages. Broad categories include tumors derived from epithelial, melanocytic, or connective tissue structures. Within each location or cell type, lesions are classified as benign, malignant, or, in certain cases, premalignant.
Benign epithelial tumors include tumors of the surface epidermis that form keratin; tumors of the epidermal appendages; and cysts of the skin.
Melanocytic, or pigment-forming, lesions are very common. One of the most frequently encountered forms is the nevus cell nevus. The term nevus has two meanings: a malformation commonly involving the entire skin layer (tissue nevus) and a benign growth of melanocytic cells (nevus cells).
Nevus cells are closely related to melanocytes and may be defined as modified neuroectodermal melanin-producing elements. The word mole, often used as a synonym for nevus, is an imprecise term because it refers to birthmarks that may or may not contain nevus cells. Neural tumors, such as neurofibromas, are related to melanocytic tumors because both are of neuroec-todermal origin.
Tumors that are derived from connective tissue include fibro-mas, histiocytomas, lipomas, leiomyomas, and hemangiomas.
Histologic evaluation
For cases in which it is not possible to distinguish clinically between benign and malignant cutaneous tumors, histopatho-logic examination is extremely important. The type of biopsy performed depends on the location, size, and nature of the lesion and on cosmetic considerations. In all cases, the clinical features must be correlated with the distinctive microscopic appearance of the tumor to confirm or exclude the diagnosis on the basis of physical examination.
Epithelial Tumors
Seborrheic keratosis
Diagnosis and Classification
Seborrheic keratosis (seborrheic wart) consists of a sharply circumscribed, rough or smooth papule or plaque that is 1 mm to several centimeters in size and dirty yellow or light to dark brown in color. The lesions often have the appearance of being stuck on and are characterized by prominent follicular plugging. They are most common in light-skinned races, first appearing in adults on the face and upper trunk and occurring more frequently with increasing age [see Figure I].
Transient eruptive seborrheic keratoses have been associated with inflammatory skin conditions, including erythroderma associated with psoriasis and drug eruptions. These keratoses tend to resolve when the skin inflammation clears.3 These transient keratoses should be distinguished from eruptive seborrheic keratoses—the sign of Leser-Trelat—which are associated with internal malignancy, particularly adenocarcinoma. The true value of the sign of Leser-Trelat as a marker of underlying malignancy is a subject of debate.
Dermatosis papulosa nigra is similar to seborrheic keratosis, but it is seen in dark-skinned races; it usually appears on the face and presents at an earlier age than seborrheic keratosis [see Figure 2].
Differential Diagnosis
The differential diagnosis of seborrheic keratosis and der-matosis papulosa nigra includes lentigo, wart, and nevus cell nevus. A biopsy may be required to rule out a pigmented basal cell carcinoma or, in the case of an inflamed seborrheic kerato-sis, malignant melanoma or squamous cell carcinoma. A shave biopsy that includes the base of the lesion may be performed before treatment with curettage.
Treatment
Curettage is a satisfactory treatment. When multiple lesions are present, anesthesia may be achieved by freezing the affected area with an ethyl chloride spray before performing curettage. For larger lesions, electrodesiccation is unnecessary and may cause scarring. Smaller lesions may be successfully treated with electrodesiccation, cryotherapy, or topical application of 50% trichloroacetic acid.
Epidermal nevus
Diagnosis
Epidermal nevus consists of closely set, skin-colored or hy-perpigmented papules that either may be localized to one side of the body and arranged in linear fashion or may be widespread. When localized, the condition is termed nevus unius lat-eris [see Figure 3]. When widespread, it is called systematized nevus. Lesions affect about one in 1,000 people; they are present at birth or appear in early childhood. The lesions have no malignant potential but may constitute a serious cosmetic problem.
Histologically, epidermal nevi exhibit hyperplasia of the epidermis; the structure or maturation of these lesions is not significantly different from that of normal epidermis. One variant, the inflammatory linear verrucous epidermal nevus, shows psori-asiform hyperplasia.
Figure 1 Verrucous, hyperpigmented lesions of seborrheic keratosis with a stuck-on appearance are present on the trunk of this patient.
Figure 2 Dermatosis papulosa nigra, as seen on the face, appears in dark-skinned races at a younger age than seborrheic keratosis.
Figure 3 Epidermal nevus with discrete and confluent brown papillo-mas is present in a somewhat linear arrangement.
Figure 4 Skin-colored or yellowish, often umbilicated papules of sebaceous hyperplasia, as seen on the forehead, may clinically resemble basal cell carcinomas.
Another variant, which is common in systematized nevi, shows granular degeneration of epidermolytic hyperkeratosis histologically. This type of epidermal nevus is a mosaic genetic disorder of suprabasal keratin. Mutations in the K10 gene are associated with lesions of the skin, whereas the normal gene is found in unaffected skin.4
Variants
The epidermal nevus syndrome involves a spectrum of different types of epidermal nevi associated with disturbances in the skeletal, urogenital, cardiovascular, and nervous systems.5 This rare syndrome is apparent at birth; the presence of widespread epidermal nevi should trigger a search for associated anomalies.
Nevus comedonicus is a variant of an epidermal nevus affecting the pilosebaceous structures; it occurs as clusters of comedonelike papules, usually in a linear pattern on the face, neck, upper arms, and trunk.5
Nevus sebaceous is a benign tumor that shows sebaceous differentiation. The lesion has a yellow hue and a granular surface and occurs in a linear pattern on the face or scalp. At puberty, nevus sebaceous may become more elevated; in adulthood, there is an associated risk of basal cell carcinoma.
Treatment
Treatment of epidermal nevi with electrodesiccation and curettage is often unsuccessful and may cause scarring. Surgical or laser removal may be indicated for localized lesions. Disturbances involving other organ systems must be evaluated and managed appropriately through a multidisciplinary approach.
Tumors of the Epidermal Appendages
There are a large number of benign tumors of the hair follicles, the sebaceous glands, and the apocrine and eccrine glands. Solitary skin tumors of these epidermal appendages are typically nonhereditary, whereas multiple neoplasms may show an autosomal dominant inheritance pattern.
Sebaceous hyperplasia
Sebaceous hyperplasia is a common clinical condition that appears as multiple skin-colored or yellowish, often umbilicat-ed papules or plaques, usually on the forehead, nose, or cheeks of persons after the fifth decade of life. These lesions consist of enlarged sebaceous gland lobules with a central dilated duct. Sebaceous hyperplasia may respond to cryotherapy with liquid nitrogen or the application of a dilute solution of trichloroacetic or bichloroacetic acid. Lesions may sometimes be confused clinically with basal cell carcinoma [see Figure 4]. In the familial form of this disorder, onset occurs in puberty; with the passage of time, the lesions increase in extent over the face, neck, and upper thorax. This condition must be distinguished from acne vulgaris, rosacea, and the angiofibromas of tuberous sclerosis. Three patients with this condition responded favorably to oral isotretinoin at a dosage of 1 mg/kg/day. To maintain the response, this dosage was tapered after 6 weeks.7 Isotretinoin is a known teratogen that cannot be given to women of childbear-ing age unless strict precautions are observed [see 2:XII Acne Vulgaris and Related Disorders].
Trichoepitheliomas
Trichoepitheliomas usually present as multiple yellowish-pink, translucent papules distributed symmetrically on the cheeks, eyelids, and nasolabial areas [see Figure5]. Often inherited as an autosomal dominant trait, the papules first appear at puberty and grow slowly for years. The gene for multiple familial trichoepitheliomas has been mapped to chromosome 9p21.8 Lesions may be confused both clinically and histologically with basal cell carcinoma, though trichoepithelioma usually shows differentiation toward the formation of hair. A single or localized trichoepithelioma may be removed by electrodesiccation and curettage. Multiple lesions are difficult to treat and may be a cosmetic problem.
Figure 5 Symmetrical papules of trichoepithelioma appear on the eyelids and nasolabial areas and may be inherited as an autosomal dominant trait.
Figure 6 Syringomas—benign tumors of eccrine ducts—are commonly seen on the face, especially on the lower eyelids.
Syringomas
Syringomas usually present in groups of multiple small papules that are distributed symmetrically over the face, especially on the lower eyelids [see Figure 6]. Eruptive syringoma, a rare condition, is characterized by widespread lesions.
Histologically, there is a benign proliferation of the eccrine ducts.
