[Clear cell acanthoma. Ultrastructural and immunohistological study].

We report a new case of a clear-cell acanthoma with an unusual location (para-anal), which was studied by electronmicroscopic and immuno-histological methods, using monoclonal antibodies. The results of this study showed that: a) the inflammatory cellular infiltrate comprised a small number of T-suppressor/cytotoxic lymphocytes and a small number of Langerhans cells, b) Langerhans cells were present in the affected epidermis in reduced numbers (2.2 p. 100) when compared to normal epidermis (4-6 p. 100), c) there was a disorder of both keratinization and epidermal differentiation as was shown by the abnormal reactivity of the tumor to monoclonal antibodies KL1 and BL7, d) human papilloma viruses do not seem to be involved in the genesis of the tumour, e) tumoral cells did not show (secretory) eccrine differentiation, f) the pemphigus antigen was present in the intercellular space of the affected epidermis.