A poroma is a benign adnexal neoplasm composed of epithelial cells that show tubular (usually distal ductal) differentiation.[1] The malignant counterpart of a poroma is referred to as porocarcinoma.[2] Poromas historically have been considered glandular adnexal neoplasms of eccrine lineage, and this view is so entrenched that the neoplasm is often referred to as eccrine poroma; however, analyses by many investigators suggest that poromas can be of either eccrine or apocrine lineage. Apocrine poromas are probably more common than those of eccrine lineage.[3, 4]
Poromas belong to the spectrum of acrospiromas, along with nodular hidradenomas, clear cell hidradenomas, dermal duct tumors, and hidroacanthoma simplex.[5, 6]
A poroma is a benign neoplasm that shows differentiation toward poroid (glandular ductal) cells. The malignant counterpart of poromas is porocarcinoma, which also shows poroid differentiation. Poromas occur only in the skin and are not known to affect any other tissues.[7, 8, 9]
The specific causes of poromas are not known. In contrast to some adnexal neoplasms of follicular lineage, poroma development has no established familial predilection.
Precise prevalence figures have not been calculated for this benign neoplasm. The worldwide prevalence for poromas is not thought to differ from that observed in the United States.
Race
Poromas are not known to have racial or ethnic predilection.
Sex
No sex predilection is known in the distribution of poromas. Males and females are equally affected.
Age
Poromas can develop in persons of any age, but onset is typically in adulthood.
The prognosis of poromas is favorable because the lesions have no known clinical significance. Even poromatosis (multiple poromas) is not known to be associated with other anomalies. The risk of malignant transformation of a poroma is minimal and is thought to be similar to that of normal skin.
A poroma usually manifests as a solitary papule or nodule.[10] Most lesions are asymptomatic, but minor pain can accompany some lesions. Rarely, the patient develops multiple poromas simultaneously, a phenomenon known as poromatosis. Multiple poromas may be of cosmetic concern and are sometimes disabling, especially if involvement of the sole is noted.
Poromas typically are asymptomatic, slow-growing, or stable nodular lesions.[11] Although most are asymptomatic, pain can be a presenting sign. Poromas are one of many types of benign adnexal neoplasms that can manifest secondarily within a nevus sebaceus.[12, 13]
Poromas typically manifest as skin-colored papules or nodules smaller than 2 cm in diameter.[14] Poromas may occasionally manifest as pigmented lesions.[15] Protuberant lesions may exhibit surface erosion or ulceration. Rarely, a poroma manifests in association with nevus sebaceus as a secondary neoplasm.[12, 13] Rabady et al reported a poroma arising on the eyelid.[16] See the image below.
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This vascular-appearing poroma presented on the tip of the toe.
Blood laboratory testing is not necessary for the diagnosis of a poroma and is not appropriate in the evaluation of an afflicted patient. The diagnosis typically cannot be made based solely on clinical findings alone, although an experienced observer may recognize the entity. The diagnosis can be fully established after surgical excision with subsequent microscopical examination by an appropriately trained and certified dermatopathologist.
Like all benign neoplasms, poromas typically show relatively sharp circumscription. Most tend to be small, although sizable tumors can be encountered. Poromas are composed of small cuboidal epithelial cells with monomorphous ovoid nuclei and inconspicuous nucleoli. The individual neoplastic cells have compact eosinophilic cytoplasm. Areas of ductal differentiation are manifested as tubules lined by a dense eosinophilic cuticle, and, sometimes, cytoplasmic vacuoles can also be seen as an indicator of luminal differentiation. Although poromas can usually be deemed benign based on circumscription and benign cytologic features, these lesions not uncommonly show small foci of necrosis en masse and a highly vascularized (granulation tissue–like) stroma, the combination of which can create concern for malignancy, especially in inexperienced observers.
Poromas manifest several different variations.
Intraepidermal poroma (historically known as hidroacanthoma simplex) represents a form of poroma in which nests of cells with tubular differentiation are confined to the surface epidermis, with no evidence of dermal involvement. This pattern of poromas can sometimes cause confusion with other entities that may exhibit an intraepidermal pattern of growth, including seborrheic keratosis and melanocytic neoplasms. See the images below.
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This intradermal poroma (dermal duct tumor) shows a sharply circumscribed border at scanning magnification. Highly vascularized and focally sclerotic ....
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At higher magnification, ductal differentiation is conspicuous.
Juxtaepidermal poroma refers to a pattern of poroma in which nests and thick cords of cells are in continuity with the epidermis but also involve the superficial dermis. The intervening stroma is highly vascularized, as described above. See the images below.
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This juxtaepidermal poroma presents histopathologically in continuity with the epidermis, creating a seborrheic keratosis-like profile.
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At higher magnification, this poroma is composed of monomorphous small keratinocytes with "cuboidal" cytomorphology.
Dermal poroma (historically referred to as dermal duct tumor) represents a pattern of poroma confined wholly to the dermis. Some intradermal poromas have relatively little stroma, while others display the highly vascularized stroma that is typical of superficial poromas.
Poromas belong to the family of tumors known as acrospiromas. These tumors all differentiate towards the acrosyringium. Other variants of acrospiroma include clear cell hidradenoma and nodular hidradenoma. Mixed patterns are common. See the image below.
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This poroma shows focal sebaceous differentiation, indicating that the lesion is of folliculosebaceous-apocrine (rather than eccrine) lineage.
Poromas are not clinically distinctive and usually cannot be diagnosed clinically; however, an experienced clinical dermatologist can sometimes recognize a poroma, especially one with a vascular appearance that develops on a volar surface.
Poromas are unrelated to activity and do not contribute to any restriction in activity, with the possible exception of a painful lesion involving the sole of the foot.
No complications are specifically associated with poromas. The surgical treatment of poromas can produce the same common complications (eg, infection, hemorrhage) associated with any minor surgical procedure.
Timothy McCalmont, MD, Director, UCSF Dermatopathology Service, Professor of Clinical Pathology and Dermatology, Departments of Pathology and Dermatology, University of California at San Francisco; Editor-in-Chief, Journal of Cutaneous Pathology
Disclosure: Received consulting fee from Apsara for independent contractor.
Specialty Editors
Richard P Vinson, MD, Assistant Clinical Professor, Department of Dermatology, Texas Tech University Health Sciences Center, Paul L Foster School of Medicine; Consulting Staff, Mountain View Dermatology, PA
Disclosure: Nothing to disclose.
Chief Editor
Dirk M Elston, MD, Professor and Chairman, Department of Dermatology and Dermatologic Surgery, Medical University of South Carolina College of Medicine
This vascular-appearing poroma presented on the tip of the toe.
This intradermal poroma (dermal duct tumor) shows a sharply circumscribed border at scanning magnification. Highly vascularized and focally sclerotic stroma is also evident.
At higher magnification, ductal differentiation is conspicuous.
This juxtaepidermal poroma presents histopathologically in continuity with the epidermis, creating a seborrheic keratosis-like profile.
At higher magnification, this poroma is composed of monomorphous small keratinocytes with "cuboidal" cytomorphology.
This poroma shows focal sebaceous differentiation, indicating that the lesion is of folliculosebaceous-apocrine (rather than eccrine) lineage.
Poroma. Courtesy of Jeffrey Meffert, MD.
This vascular-appearing poroma presented on the tip of the toe.
This intradermal poroma (dermal duct tumor) shows a sharply circumscribed border at scanning magnification. Highly vascularized and focally sclerotic stroma is also evident.
At higher magnification, ductal differentiation is conspicuous.
This juxtaepidermal poroma presents histopathologically in continuity with the epidermis, creating a seborrheic keratosis-like profile.
At higher magnification, this poroma is composed of monomorphous small keratinocytes with "cuboidal" cytomorphology.
This poroma shows focal sebaceous differentiation, indicating that the lesion is of folliculosebaceous-apocrine (rather than eccrine) lineage.
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