RESUMO
BACKGROUND: Clear cell acanthoma usually appears as an asymptomatic nodule on the leg. It has an unusual clinical feature in that it is presented as chronic eczema on the areola. The origin of clear cell acanthoma is not yet clear, although many hypotheses have been proposed, including a benign neoplasm or an inflammatory dermatosis. OBJECTIVE: In this study, clear cell acanthoma on the areola showing clinically eczematous features were analysed by immunohistochemical techniques, using antibodies against cytokeratin 16, involucrin and PCNA and compared with psoriasis and squamous cell carcinoma. METHODS: Using the immunohistochemical method with formalin-fixed, paraffin-embedded sections, we analysed the expression of cytokeratin 16, involucrin and PCNA in biopsy specimens of 6 cases of clear cell acanthoma on the areola, 5 cases of psoriasis, and 5 cases of squamous cell carcinoma. RESULTS: The expression of cytokeratin 16 was detected in spinous and granular layers in all cases of clear cell acanthoma and psoriasis and three cases of squamous cell carcinoma. Psoriasis showed slightly higher immunoreactivity than clear cell acanthoma and squamous cell carcinoma, but this difference was not statistically significant (p=0.142). The expression of involucrin was detected in spinous and granular layers in all cases of clear cell acanthoma, psoriasis, and squamous cell carcinoma. The immunoreactivities were similar. The expression of PCNA was detected in basal and spinous layers in two cases of clear cell acanthoma, four cases of psoriasis, and five cases of squamous cell carcinoma. The expression of PCNA was higher in psoriasis and squamous cell carcinoma than in clear cell acanthoma, and this difference was statistically significant (p=0.034, p=0.004). CONCLUSION: Clear cell acanthoma on the areola may result from increased psoriasis-like inflammatory proliferation and accelerated differentiation of keratinocytes.