[Melanomas of the anorectal area (problems of histogenesis, morphogenesis and histological diagnosis)]

Morphogenesis, histology, specific function of 17 anorectal melanomas were studied. The source of the tumour are melanocytes of the stratified squamous epithelium of the anal canal. An important part of morphogenesis consists of appositional growth and emergence of microinvasion foci associated with it beyond the borders of the primary focus. By the features of histogenesis, morphogenesis, and specific function, melanomas of this localization show no principal differences from skin melanomas. Diagnostic difficulties are associated with the possibility of occurrence of anaplastic nonpigmented forms. This would require to employ most informative methods for melanogenesis detection (Masson-Hamperl's method and electron microscopic examination) and to search for atypical marginal melanocyte proliferation beyond anatomical and microscopic borders of the primary tumour as manifestations of its appositional growth.