[Apocrine poroma. A relatively little known skin tumor with multilineage differentiation]

Poromas were originally classified as eccrine tumors which predominantly consist of poroid ductal cells and differentiate in the direction of sweat gland ducts. However, there have now been many reports on poromas with additional differential characteristics differentiating in the direction of sebaceous and/or apocrine glands and/or hair follicles. These tumors have been termed apocrine poromas. Multilineage differentiation within a poroma can be explained by the embryological association of the sweat duct with the so-called folliculo-sebaceous-apocrine unit. The clinical and histopathological features of apocrine poromas are reviewed in comparison to classical eccrine poromas by taking into account seven own cases of apocrine poroma and a review of the literature. It is important for histopathologists not to confuse apocrine poroma with other tumors with multilineage differentiation. Apocrine poroma needs to be distinguished from sebaceoma and from basal cell carcinoma with sebaceous differentiation, in particular, because these tumors have therapeutic consequences for the patient. The main histopathological differences between apocrine poroma, sebaceoma and basal cell carcinoma with sebaceous differentiation are explained.