Squamous cell carcinoma arising from an epidermal cyst: A case series of 5 cases and literature review.

Epidermal cysts are among the most common benign subcutaneous tumors and can undergo malignant transformation at a rate of 0.1%-2.2%. However, there are limited studies that summarize the radiological characteristics of malignant lesions arising from epidermal cysts. This study aims to report 5 patients diagnosed with malignant transformation of epidermal cysts, emphasizing the importance of radiological assessment in distinguishing benign from malignant lesions. The five patients were in their 50s to 80s, and all patients were male. The duration from the time a patient recognized a lesion to diagnosis ranged 7 and 60 years. One patient had a history of injury 18 years ago. The longest diameter of the lesion ranged from 7 to 25 cm. The lesions tended to have cystic lesions with nodules on the wall on the T2-weighted image, isointensity to muscle on the T1-weighted image, the enhanced wall and nodules on the contrast-enhanced T1-weighted image, and restricted diffusion. There were 2 important radiological findings that are associated with malignancy: the large size of the cyst and a well-enhanced nodule on the cyst wall. Additionally, the long-standing presence of the lesion may support making a diagnosis of malignant transformation. When malignancy is suspected in an epidermal cyst, radiological assessment and needle biopsy play essential roles in avoiding unplanned excision and guiding appropriate surgical management.