Porocarcinomas are malignant counterparts to the far more common benign tumors of the eccrine sweat gland's acrosyringium, i.e. poromas. As currently viewed, there are 4 poroma variants based on their predominant cell types and extent of the their tumor tissues presence in the epidermis and dermis: 1) Hidroacanthoma simplexe poromas are confined to the epidermis, i.e. uppermost layer of the skin. 2) Dermal duct poromas are confined to the dermis, i.e. layer of skin between the epidermis and subcutaneous tissues. 3) Hidradenomas have recently been sub-classified into two groups; 95% are termed clear cell hidradenomas and have features suggesting that they derive from apocrine sweat glands while the remaining 5% are termed poroid hidradenomas and have features suggesting that they derive from eccrine sweat glands. And 4) eccrine poromas are eccrine sweat gland tumors that consist of three cell types (see the histopathology section of Poromas) and are primarily located in the epidermis and superficial dermis. Poromas may have 2 or more of these variants in the same tumor tissue and the variants typically have histopathology findings that are not clearly distinguishable from each other. PCA tumors may arise from one of these longstanding poromas (in one study this occurred in 18% of cases) but more commonly appear to develop independently of any precursor poroma.
