Poromas are rare, benign, cutaneous adnexal tumors. Cutaneous adnexal tumors are a group of skin tumors consisting of tissues that have differentiated (i.e. matured from stem cells) towards one or more of the four primary adnexal structures found in normal skin: hair follicles, sebaceous sweat glands, apocrine sweat glands, and eccrine sweat glands. Poromas are eccrine or apocrine sweat gland tumors derived from the cells in the terminal portion of these glands ducts. This part of the sweat gland duct is termed the acrosyringium and had led to grouping poromas in the acrospiroma class of skin tumors (syringofibroadenomas and syringoacanthomas are classified as acrospiromas). Here, poromas are regarded as distinct sweat gland tumors that differ from other sweat gland tumors by their characteristic clinical presentations, microscopic histopathology, and the genetic mutations that their neoplastic cells have recently been found to carry.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 simplex 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.
Rarely, individuals present with multiple poromas either in one or widespread areas; these cases are termed poromatosis.Poromas present more commonly in: pregnancy; patients treated with electron therapy for mycosis fungoides; sites of chronic radiation dermatitis caused by long-term radiation exposure; patients who received chemotherapy with or with radiation therapy (these patients have often presented with poromatosis); individuals with underlying skin conditions such as hypohidrotic ectodermal dysplasia and Bowen’s disease (i.e. a form of squamous cell carcinoma that is localized to the outermost layer of the skin); and skin plaques of individuals with the congenital disease, nevus sebaceous.Poromas are usually slow growing and asymptomatic but some individuals report that their lesions are itchy, mildly tender, or  painful. An existing poroma that develops spontaneous bleeding, ulceration, sudden itching, pain, or rapid growth over a short period of time may indicate that it has become a cancerous porocarcinoma. These cancers may metastasize to local lymph nodes, nearby or distal skin sites, bones, bladder, breast, retroperitoneum, ovary, liver, lung, brain, or stomach. However, the progression of a poroma to a porocarcinoma is very rare, i.e. less than 1% of cases. Histopathology
Microscopic histopathological examinations of the tumor tissues of all poroma variants stained with hematoxylin and eosin dyes reveal: a) basophilic "poroid cells" (i.e. small, cuboid-shaped cells with oval nuclei which resemble cells in the peripheral layer of the distal portion of eccrine sweat gland ducts) that may form cords and broad columns extending downward from the epidermis; b) larger cuticular cells (i.e.