Sebaceous carcinoma is a rare cutaneous malignancy that frequently mimics other dermatologic conditions. Extraocular subtypes are uncommon, but when present are frequently located in the head and neck region. Herein, we present a patient with a rapidly growing upper back mass eventually diagnosed as sebaceous carcinoma and managed with wide surgical excision. Currently, sparse literature exists to guide management of such patients. This case highlights not only the diagnostic challenges of sebaceous carcinoma, but also the need for further studies to investigate therapeutic interventions and long-term outcomes.

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.