Ideas in pathology. Malignant melanoma in situ: the evolution of a concept.

For clinical dermatologists, proliferations of melanocytes confined to the epidermis (and epithelial structures of adnexa) are either flattish melanocytic nevi (junctional type) or flat lesions (macules and patches) of malignant melanoma (malignant melanoma in situ). The same should be true for histopathologists. During the past 30 years, however, histopathologists have avoided making specific diagnoses of malignant melanoma in situ by utilizing a variety of nondiagnostic, euphemistic descriptions for it such as melanotic freckle of Hutchinson, melanosis circumscripta precancerosa of Dubreuilh, active junctional nevus, lentigo maligna, atypical melanocytic hyperplasia, melanocytic dysplasia, and melanocytic intraepithelial neoplasia. Each of these terms evades a specific diagnosis of malignant melanoma in situ, a diagnosis than can, and should, be made clinically and histopathologically if reliable criteria are used. The legitimacy of a concept of malignant melanoma in situ in the context of historical perspective and the importance of that concept for management of patients are the themes of this essay.