Introduction
Eccrine poromas are benign adnexal neoplasms that typically arise on acral skin, particularly the palms and soles, where eccrine sweat glands are most concentrated.1 Although the classic presentation is acral, poromas have been reported on nonacral locations.1,2 Atypical clinical and histopathologic morphologies can add a diagnostic challenge to such cases. Here we present a rare case of an eccrine poroma with atypical features located on the buttock, an uncommon site for this tumor, and highlight the diagnostic considerations when evaluating these tumors.
Case report
A 52-year-old otherwise healthy man presented with a slowly enlarging, intermittently tender nodule on his right gluteal region. The lesion had been present for 8 months and was initially presumed to be an inflamed epidermal inclusion cyst. A physical examination revealed a 1.2 cm firm, dome-shaped, erythematous nodule with central crusting located on the right buttock (Fig 1). There was no regional lymphadenopathy and the patient denied systemic symptoms. A shave biopsy demonstrated a well-circumscribed proliferation of poroid and cuticular cells extending from the epidermis into the dermis with ductal differentiation (Figs 2 and 3). Focally, there was mild nuclear pleomorphism and hyperchromasia, with up to 3 mitoses/10 high-power fields (Fig 4). Immunohistochemistry was positive for epithelial membrane antigen and carcinoembryonic antigen in ductal structures, with a low Ki67 proliferation index (<10%), supporting the diagnosis of a poroma with atypical features rather than porocarcinoma. Given the involvement of tissue edges and the known potential of adnexal tumors to recur if incompletely excised, the lesion was removed by complete surgical excision. At 12-month follow-up, there was no recurrence or evidence of malignant transformation.
Fig 1.
1.2 cm firm, dome-shaped, erythematous nodule with central crusting located on the right buttock.
Fig 2.
A well-circumscribed tumor was noted with broad epidermal connections. The lesional cells demonstrated poroid cytology. Hematoxylin and eosin, 76 × magnification.
Fig 3.
Duct formation was present throughout the tumor. Hematoxylin and eosin, 144 × magnification.
Fig 4.
Focal areas demonstrated mild nuclear pleomorphism, hyperchromasia, and increased mitotic figures. Hematoxylin and eosin, 75 × magnification.
Discussion
Poromas most commonly occur on acral sites; nonacral presentations, such as on the buttocks, are unusual and expand the clinical spectrum of these neoplasms.1,2 In such atypical locations, they may not be readily suspected clinically. In our case, the lesion was initially thought to represent an inflamed epidermal inclusion cyst. Histopathologically, poromas are well-circumscribed tumors extending down from the epidermis consisting of monomorphic, small, cuboidal cells punctuated by ducts. Poromas can demonstrate variable degrees of nuclear pleomorphism, hyperchromasia, and occasional mitotic activity, which raises the differential diagnosis of porocarcinoma.3 Careful evaluation of architecture and cytologic features remains the cornerstone of distinguishing between benign and malignant poroid neoplasms. In our case, the sharp circumscription, ductal differentiation, only mild cytologic atypia, and low proliferation index supported a benign diagnosis. Ancillary studies, including immunohistochemistry, may provide supportive evidence such as confirming ductal differentiation (epithelial membrane antigen, carcinoembryonic antigen) or assessing proliferation (Ki67). However, immunohistochemical is not definitive in separating benign from malignant poroid neoplasms, and this limitation contributes to the diagnostic challenge of adnexal tumors.4 Recent molecular insights have added further understanding, however were not obtained in our case. Recurrent YAP1::MAML2 (Yes-associated protein 1–mastermind-like protein 2) and YAP1::NUTM1 (Yes-associated protein 1–nuclear protein in testis midline carcinoma family member 1) fusions have been identified in both poromas and porocarcinomas, suggesting a shared pathogenetic pathway.5 NUT immunohistochemistry can serve as a surrogate for detecting YAP1-NUTM1 fusions, while additional fusion variants such as YAP1::NR4A3 (Yes-associated protein 1–nuclear receptor subfamily 4 group A member 3) and YAP1::NCOA2 (Yes-associated protein 1–Nuclear receptor coactivator 2) highlight the genetic heterogeneity of poroid neoplasms.6 Complete surgical excision with histologically negative margins is recommended, especially in tumors with atypical features, to prevent recurrence or progression.3
Conflicts of interest
None disclosed.
Footnotes
Funding sources: None.
Patient consent: The authors obtained written consent from patients for their photographs and medical information to be published in print and online and with the understanding that this information may be publicly available. Patient consent forms were not provided to the journal but are retained by the authors.
IRB approval status: Not applicable.
References
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