Hidradenocarcinomas: a brief review and future directions.

Hidradenocarcinomas are rare, aggressive skin adnexal tumors of sweat gland origin that demonstrate a high potential for local recurrence, metastasis, and poor outcome. These neoplasms can derive from preexisting clear cell hidradenomas but more commonly appear de novo, with the molecular events responsible for the pathogenesis currently unknown. Historically, diagnosis has been difficult because of the few cases, inconsistent nomenclature, variable morphology of cells that compose the neoplasm, and confusion with other visceral metastatic tumors. Presentation is generally benign with an indolent clinical course that typically includes local and multiple recurrences. Despite wide-excision surgery, disease at regional lymph nodes and metastatic sites is common and linked to decreased survival. Currently, molecular markers of pathogenesis as well as effective forms of adjuvant chemotherapy are lacking. Future studies are required to identify the histopathologic and immunohistochemical features, which may facilitate diagnosis and foster development of molecularly targeted forms of adjuvant therapy.