Patient Presentation A 46-year-old male presented with a small growth, which he had for at least 10 years on the left sole. The lesion was asymptomatic, but it was accidentally slightly traumatized a few days prior to his presentation. The patient’s past medical, surgical and family histories were non-contributory. On examination of the left sole, there was a 5-mm x 5-mm slightly erythematous firm papule with a smooth central area and a distinguished collarette of skin on the periphery localized to the left sole toward the lateral aspect of the heel. On palpation the papule seems to be firm and well circumscribed, and no fluid or other content could be extruded on pressure. The rest of the examination was within normal limits. Diagnosis: Eccrine Poroma The term “poroma” refers to benign neoplasms with “poroid” or terminal ductal differentiation. The first eccrine poroma (EP) was described 50 years ago by Goldman, Pinkus and Rogin as a tumor of sweat gland origin.1 Seven years later, Pinkus and Mehregan described a malignant variant termed porocarcinoma.2 This detailed description included a comparison and differentiation from Paget’s disease based on characteristics such as the lack of tonofibrils and the presence of glycogen noted in EPs. Although EPs are considered benign, reports have suggested porocarcinomas exist as a progression of EPs.3 The first porocarcinoma presentation included lymphedema of the lower extremities with multiple widespread metastatic nodules, thus emphasizing the importance of recognizing and diagnosing such seemingly benign lesions.2Etiology and Prevalence The pathogenesis of EPs remains unknown. However, reports have noted associations with scars,4 radiation5 and trauma.6EPs typically present after 40 years of age, with only eight cases reported in patients 18 years or younger.7 The prevalence of EPs has not been reported. No relation has been noted with race, and no inheritance pattern has been described.Clinical FeaturesPhysical appearance of EP and descriptions vary. Typical appearance may consist of a 2-mm to 12-mm soft sessile nodule protruding from a circular depression. However, an EP can be an erythematous, pink or cyanotic papule or nodule. EPs can also be rubbery, or a verrucus-like plaque, or even an ulcerative nodule. These lesions are often moist, exophytic and can reach 3 cm in diameter with a smooth or crusted surface. A keratotic collar may also be noted, as well as a moat-like depression. Other variants reported include pigmented EPs, in which pigmentation is associated with melanocyte enhancing endothelin-1 expression.8The majority of EPs occur on the soles of the lower extremities, but can also be found on palms, trunk, upper extremities, and head and neck region.3 When EP lesions appear in clusters, this is referred to as “poromatosis.”9 EPs tend to be asymptomatic but bleed with trauma, and thus make this the common clinical presentation. Itching or pain should raise the suspicion of malignancy.10DiagnosisDiagnosis is confirmed primarily with histological analysis. On noting a lesion with features of EPs, the differential diagnosis should include squamous cell carcinoma (SCC), basal cell carcinoma (BCC), malignant melanoma, amelanotic melanoma, botryomycoma, fibrokeratoma and pyogenic granuloma. A thorough workup should be preformed and must include a biopsy. Even lesions with minimal physical abnormalities have been reported as malignant.11 Interestingly, although a lesion clinically appearing as an EP may be a porocarcinoma, the opposite is also true in which a lesion clinically mimicking a porocarcinoma type lesion may be EP,12 emphasizing the importance of complete excisional biopsy and careful analysis. Pathogenesis and Histology On biopsy, EP is noted as a solid tumor. A clear circumscribed margin exists between adjacent normal epidermal keratinocyte and the EP population of smaller cuboidal cells with darker monomorphous nuclei and scant cytoplasm. The deeply basophilic oval nuclei give these cells an overall basaloid nature. However, unlike BCC, these cells do have glycogen, do not palisade, and do not express transcriptional factor Gli1.13 EPs may have a highly vascular polymorphous pattern and have been known to mimic amelanotic melanoma.14 This highly vascular stroma can also mimic pyogenic granuloma, and is differentiated by the high glycogen content. EP cells may have cystic spaces devoid of any lining. These cystic spaces, pseudohorn cysts, can make differentiation from seborrheic keratosis difficult.On closer examination, cells are noted to be united by intracellular bridges that are less distinct than those in SCC. Rarely are mitotic figures seen, and despite the low cell proliferation, nests of necrosis may be seen. Individual tumor nests can be separated by normal epidermis thus mimicking hydroacanthoma simplex.EP staining shows strongly PAS positive cells due to the high glycogen content. Ductal differentiation can be confirmed by CEA staining. Eccrine enzymes also predominate. Phytohemagglutinine (PHA) can be used to differentiate EPs from porocarcinoma as PHA doesn’t stain the former. From a genetic perspective, and also supporting the theory of progression to carcinogenesis, both EPs and porocarcinomas express p53;15 however, the stabilization of the produced p53 seems to be the differentiating factor.16Immunohistochemical studies have attempted to elucidate the histogenesis of poroid neoplasms. However, debate still exists. For example, based on histochemistry and electron microscopy studies, EP was thought to be derived from the basal cells (outer cells) of the intraepidermal portion of the eccrine duct, also known as the acrosyringium.17 However, other immunochemical studies speculate that EPs originate via the proliferation and expansion of ductal and/or epidermal basal cells.18, 19 Overall, a trend has arisen to separate poromas based on origin as apocrine or eccrine poromas.20 Currently, various names exist for EPs depending on histology. Intraepidermal poromas, also known as hidroacanthoma simplex, are nests of cells with tubular differentiation confined to the epidermis. Juxtaepidermal poromas are noted as nests of thick cords of cells in continuity with the epidermis and involving the superficial dermis. Dermal poromas, also known as dermal duct tumors, are confined to the dermis. ManagementTreatment of choice is surgical excision. Recently, alternate treatments have been attempted including case reports on use of imiquimod cream (Aldara).24 As EP is considered benign, prognosis is good without complications. No known prevention exists.Our patient underwent excision of the lesion followed by layered closure. No complications were noted. At 6-month follow-up, no reoccurrence was noted. Disclosure: The authors have no conflict of interest with any subject matter discussed in this month’s column.