A rare cutaneous neoplasm that occurs in the elderly. It develops more frequently in women and predominantly involves apocrine gland-bearing areas, especially the vulva, scrotum, and perianal areas. The lesions develop as erythematous scaly patches that progress to crusted, pruritic, erythematous plaques. The clinical differential diagnosis includes squamous cell carcinoma in situ and superficial fungal infection. It is generally thought to be an adenocarcinoma of the epidermis, from which it extends into the contiguous epithelium of hair follicles and eccrine sweat ducts. (DeVita Jr et al., Cancer: Principles & Practice of Oncology, 3d ed, p1478)