Hidradenocarcinoma of the Hallux: Report of a Rare Diagnosis in an Atypical Location.

Summary: BACKGROUND: Hidradenocarcinoma (HAC) is a rare malignant neoplasm of the sweat glands, associated with a high risk of local recurrence and metastasis. The diagnosis is challenging due to its rarity, nonspecific clinical presentation, and heterogeneous histological features. In this case report, we describe a 37-year-old patient with an asymptomatic tumor of 3 centimeters on the left hallux for 15 years, with histopathological examination revealing hidradenocarcinoma. DISCUSSION: This rare and aggressive neoplasm can affect various anatomical regions, especially the head and neck. According to our review, this is the first reported case of HAC on the hallux. Its clinical presentation may be nonspecific, and histology can be difficult to distinguish from hidradenoma. This case highlights the importance of a complete histological evaluation of the tumor for the diagnosis of malignant adnexal neoplasms and contributes to the limited literature on reported HAC cases.