Aggressive Squamous Cell Carcinoma Developing in a Giant Epidermal Cyst of the Abdomen

In 2006, a 48-year-old Japanese woman with a giant epidermal cyst (EC) on her abdomen for over a decade developed aggressive squamous cell carcinoma (SCC) within the cyst. The EC, which had rapidly enlarged to 9.2 × 6.6 cm in the last 6 months, was excised with clear margins, but the patient still developed lung metastasis four months after surgery and died 10 months post-operation from respiratory failure due to widespread metastasis. This case highlighted the risk of rapid systemic metastasis from SCC developing in long-standing ECs, especially following rapid enlargement, and underscored the importance of complete excision and vigilant follow-up. Prior to this case, only 10 similar cases had been reported, with ECs present for 2 to 132 months and sizes ranging from 1 to 10 cm before SCC development.