Apocrine adenocarcinoma in the setting of apocrine hidrocystoma of the leg.

Apocrine hidrocystoma is a benign, cystic lesion often presenting in the periorbital region. Apocrine adenocarcinoma is the rare, malignant counterpart occurring mainly in the axilla and anogenital region. There is a paucity of literature on both entities and co-occurrence has been reported in only 5 cases. We present the case of a 48-year-old man with a history of total body irradiation for chronic myelocytic leukemia, diabetes mellitus, and obesity who presented with a calf mass of two years' duration. Epidermal inclusion cyst was presumed and excisional biopsy was carried out. Pathologic analysis revealed apocrine adenocarcinoma in the setting of a precursor apocrine hidrocystoma. Our patient's unique altered immunity and the direct effects of irradiation on the local microenvironment may have resulted in his rare presentation of co-occurrence of apocrine adenocarcinoma within an existing apocrine hidrocystoma. To our knowledge, our patient is the first reported patient with this presentation in the lower extremity.