The purpose of our work is to alert fellow pathologists to criteria for identification of melanoma in prepubescent children and to be able to accomplish that even in the absence of any clinical information, including the age of a patient. In brief, a melanoma in a child can be distinguished from a Spitz's nevus by paying heed carefully to both architectural and cytological attributes (Table 6).

In our experience, the histopathologic character of melanoma that arises de novo in prepubescent children is markedly different from that which develops in adults. To delineate the distinguishing features, one last time for emphasis, melanomas in prepubescent children tend to be vertically oriented, very thick (often extending into the subcutaneous fat), not strikingly asymmetrical, and devoid of a prominent in situ component. The melanocytes are arranged mostly in nests and fascicles that become confluent to form a sheet characterized by little, if any, intervening dermis or fat. Adnexal structures usually are absent. Melanin is distributed very unevenly. The upper part of a melanoma in a prepubescent child may resemble closely a Spitz's nevus by virtue of hyperkeratosis, hypergranulosis, adnexal epithelial hyperplasia, edema of the papillary dermis, telangiectases, fascicles of melanocytes at the dermo-epidermal junction oriented vertical to the skin surface, a cleft between some fascicles and adjacent keratocytes, and melanocytes whose shape is plump oval, spindled, or polygonal. At high magnification, the cytologic features are a caricature of those of Spitz's nevus, namely, more nuclear pleomorphism, more heterochromasia, more prominent nucleoli, more mitotic figures, more abnormal mitotic figures, and more mitotic figures near the base of the neoplasm, where infiltrates of lymphocytes tend to be most dense. Even though the intraepidermal component of these thick melanomas in prepubertal children may be paltry, it must be assumed that at one stage in their chronologic course they were situated wholly in situ. If a biopsy had been taken when the lesion was flat, sections of tissue from the specimen would show features of melanoma confined to epidermal and adnexal epithelium.