Perineal Squamous Cell Carcinoma Arising in an Epidermal Cyst

A 90-year-old Japanese woman who had been aware of a subcutaneous mass on the right perineal region for 5 years was referred to our hospital for further examination and treatment because of the rapid growth of the mass and bleeding that began 3 months earlier. A biopsy of the mass revealed a diagnosis of well-differentiated squamous cell carcinoma. On preoperative examination, the tumor was 90×40 mm in size and was suspected to have partially invaded the levator ani muscle and external sphincter. Since a preoperative cardiac evaluation indicated severe aortic stenosis, we performed transcatheter aortic valve implantation. A radical resection was then performed with general anesthesia. The skin and subcutaneous tissue defects were reconstructed with a posterior gluteal-thigh propeller flap, and a sigmoid colostomy was created. The patient had a good postoperative course and was transferred to a rehabilitation facility 28 days after the surgery. Epidermal cysts are a common benign tumor, and clinicians should keep in mind that these cysts can become malignant.