Squamous cell carcinoma arising from a huge buttock epidermal cyst without skin lesion: A case report

INTRODUCTION: Epidermal cysts are common lesions on the surface of the body. However, squamous cell carcinomas (SCCs) arising from epidermal cysts are rare and even rarer without skin lesions, such as ulcers. PRESENTATION OF CASE: A 66-year-old male presented with a 10-cm sized mass on the left buttock without skin lesions. The patient was aware of the existence of the lesion 10 years prior. However, recently, the mass increased in size causing pain. Surgical resection was decided based on the suspicion of an epidermal cyst. Histopathological examination revealed SCC arising from an epidermal cyst. Additional complete resection was performed. No recurrence was observed 1 year after the surgery. DISCUSSION: The clinical and pathophysiological characteristics of malignant transformation of epidermal cysts have not yet been fully elucidated. However, the lesions are characterized by long-lasting and rapid growth later, with the presence of a keratinous cystic tissue structure similar to an epidermal cyst. Part of the tumor is non-malignant, which is adjacent to the area of atypical cell proliferation. The present case had all the above four characteristics and was therefore diagnosed as SCC arising from an epidermal cyst. CONCLUSION: Even if a palpable mass shows benign findings on physical examination, malignant transformation should be considered if the mass grows rapidly in size and is accompanied by symptoms such as pain.