[Eccrine poroma. A clinico-pathologic and immunohistologic study with special reference to tumor cell differentiation].

In this study 15 eccrine poromas were analysed clinically, histologically and immunohistologically. They were all solitary lesions, showing a predilection for the head and neck. In none of the tumours was diagnosis possible on the basis of clinical examination. Histomorphologically, eccrine poromas were characterized by aggregations of neoplastic cells continuous with the epidermis. The neoplasms consisted of two cell types, poroid and cuticular. Poroid cells predominated, while cuticular cells were only found in small foci, sometimes showing tubular differentiation. Immunohistologically, most of the tumour cells showed a cytokeratin pattern (CK1, 5, 10, 11+, CK1-19+) favouring differentiation toward the abluminal cell of the dermal eccrine duct rather than toward the abluminal cell of the intraepidermal segment of the eccrine duct. Only a small proportion of cells revealed the immunohistological features of the abluminal cell of the intraepidermal duct (CK1+, CK1, 5, 10, 11+, CK1-19+). In addition, cuticular cells showed differentiation toward the luminal cell of the eccrine duct (CK19+, CK1, 5, 10, 11+, CK1-19+). Simple-type cytokeratins such as CK7 and CK18 were not expressed. In conclusion, our findings favour the hypothesis that ascribes the origin of eccrine poroma to a pluripotential stem cell of the transitional zone between the dermal and the intraepidermal segments of the eccrine duct.