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Case Reports

Abstract

Eccrine carcinoma, a rare type of skin adnexal malignancy, typically manifests as a locally invasive, solitary lesion in the head and neck area. Instances of eccrine carcinoma originating in the extremities are exceedingly uncommon. Due to its rarity, there is limited consensus on histologic features and immunohistochemical results, making accurate diagnosis challenging and misdiagnosis a potential concern.

A 56-year-old male presented with a rapidly growing, painful lesion on his left great toe. Imaging revealed soft tissue swelling without other concerning features. Biopsy results showed a dermal-based tumor composed of nests and cords of atypical epithelial cells forming ductal structures. The individual tumor cells have fine chromatin with prominent nucleoli and eosinophilic cytoplasm.

Immunohistochemical staining demonstrated diffuse positivity for p63 and, as well as focal positivity for CK7. Notably, the tumor was negative for S100 protein, estrogen receptor (ER), progesterone receptor (PR), and androgen receptor. Whole-body PET/CT did not reveal evidence of distant metastasis. Consequently, amputation of the great toe was performed, and no recurrences or metastases were observed during the 6-month follow-up.

Regarding the location and malignant histologic features, the differential diagnosis included digital papillary adenocarcinoma. However, the presence of diffuse atypical epithelioid cells in nests and lobules with lack of papillary proliferations, along with the absence of immunoreactivity for S100, ER, and PR, led to the consideration of eccrine ductal carcinoma as the most plausible diagnosis. Due to the potential for recurrence and metastasis, it is crucial to recognize this rare disease entity even in unusual locations.