Squamous cell carcinoma arising from a long-standing epidermoid cyst of the back

Epidermoid cysts are commonly encountered benign lesions in the field of plastic surgery, but their malignant transformation into squamous cell carcinoma (SCC) is extremely rare.A 68-year old woman with a cystic mass on her left lower back presented to our department.We excised the lesion under the suspicion of an epidermoid cyst or metastatic colon cancer based on the patient's medical history.The skin defect was covered with a split-thickness skin graft, and histopathological evaluation revealed the presence of SCC.Because of the low incidence of SCC arising from an epidermoid cyst, the mechanism of transformation of such cysts to SCC and the prognosis of this condition have not yet been well established.We therefore share the details of this rare case to contribute to the growing base of knowledge about SCC that arises from an epidermoid cyst.