Porom eccrinesD23.L

Pinkus, 1956. Originally, poroma was defined by Pinkus et al. as a poroid (terminal ductal) differentiated epithelioma of eccrine origin. Further reports have described cases with apocrine, sebaceous, and follicular differentiation (Horenstein MG et al. 2018).

Eccrine poromas may develop intraepidermally (intraepidermal poroma - historical name: hidroacanthoma simplex, see also Borst-Jadassohn phenomenon).

A second type grows into the papillary epidermis in broad adherence to the surface epithelium, broad-based solid or reticular (juxtapidermal eccrine poroma).

A third type is dermal eccrine poroma, which spreads quite predominantly in the dermis, without a broad relationship to the surface epithelium. The term "dermal duct tumor" was also commonly used for dermal eccrine poroma.

Mainly localized on the soles of the feet, palms of the hands, less frequently on the head and neck, also on the remaining integument (Sawaya JL et al. 2014). Exceptional is the multiple occurrence (eccrine poromatosis).

Little characteristic clinical picture. Solitary, asymptomatic, sharply circumscribed, raised, 1-4 mm to 3 cm in size, sometimes pedunculated, possibly slightly reddened, unpigmented, broad-based nodule or lump or a corresponding plaque. The usually unpigmented tumor is skin-colored to brownish-red in color. Especially in cystic forms, a blue-black discoloration may occur as a result of hemorrhage. Eccrine poromas may occur together with a nevus sebaceus or develop secondarily in a n. sebaceus. The rare occurrence of multiple poromas in acral skin is called poromatosis.

Demarcated compact or reticular, uniform cell proliferation from cuboidal keratinocytes with small, hyperchromatic nuclei and a uniform eosinophilic, glycogen-rich (PAS-positive) cytoplasm. In sections, light cell complexes are also found. The poroma may express tubular structures (less commonly ductal). In the case of ductal differentiation, carcinoembryogenic antigen (CEA) is detectable. In tubular structures, decapitation phenomena can often be detected (indicating an apocrine genesis of this poroma). The tumor parenchyma is surrounded by a hyalinized stroma.

Circumscribed beet-like cell necrosis in malignant (not in eccrine poroma!) tumors is frequent (necrosis en masse) and should be regarded as an indication of their malignancy, since perfusion is no longer guaranteed due to rapid growth, resulting in a reduced supply of cell necrosis. Focally, ductal structures differentiate. Rare are sebocytic differentiations at the base of the tumor.

It is a histological incidental diagnosis. Excision with a safety margin of 1-2 mm is curative. Alternatively, there are single case reports that topical therapy with 5% imiquimod (3x/week for 4 weeks) is also effective.

Favourable; rarely a malignant degeneration into a porocarcinoma can be observed.

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