Periungual hidradenocarcinoma mimicking squamous cell carcinoma: A rare presentation with dermatoscopic findings

Dear Editor, Hidradenocarcinoma is a rare, adnexal tumor that arises from eccrine sweat glands with a high potential for local recurrence, metastasis, and poor outcome. It can derive from preexisting hidradenomas but most often arises de novo. Hidradenocarcinoma is most often located on the head and neck, and rarely on the extremities. Herein, we report a case of periungual hidradenocarcinoma with dermatoscopic findings, mimicking well-differentiated squamous cell carcinoma (SCC). A 69-year-old female presented with a 2-year history of a gradually enlarging periungual mass that had been tender and bleeding in recent months. Trauma history was unremarkable. Physical examination revealed a hyperkeratotic-scaly nodular lesion with a size of 15 × 10 mm on the ulnar aspect of the right thumb, also mildly invading the nail (Figure 1A). Dermatoscopic examination showed a keratin mass with hemorrhagic spots and fiber sign over a nodular lesion that invaded the ulnar site of the right thumb nail. The peripheral flat part of the lesion showed clustered dotted vessels, white circles, and pink and white structureless areas (Figure 1B,C). Histopathological and immunohistochemical examination of the skin biopsy showed a diagnosis of hidradenocarcinoma (Figure 2A-I). Preoperative 18-fluorodeoxyglucose PET-CT scan to evaluate the possibility of regional or distant metastasis showed no evidence of metastasis. The tumor was excised with 6 mm margins, and the nail