A Rare Transformation of Epidermoid Cyst into Squamous Cell Carcinoma: A Case Report with Literature Review.

BACKGROUND Epidermoid cysts are the most common benign skin lesions that can occur anywhere on the body, and frequently occur on the face, scalp, neck, and trunk. Typically, patients are asymptomatic, and the lesions present as firm skin-colored nodules filled with keratinous or sebaceous materials that are formed by cystic expansion of the epidermal epithelium. Malignant transformation is rare in epidermoid cysts. CASE REPORT This is a case report of a 77-year-old male Caucasian patient who presented with an epidermoid cyst on the left parietal area. Due to high suspicion, the cyst was surgically excised and sent to pathology which resulted in discovery of malignant squamous cell carcinoma with unclear margins. Aimed at obtaining clear margins, a wide excision was performed, which revealed clean margins and absence of residual cancerous cells. The patient recovered well without major complications. CONCLUSIONS Although the prevalence of epidermoid cysts is high, malignant transformation of epidermoid cysts into squamous cell carcinoma is rare. Due to its scarcity, the exact pathophysiology of malignant transformation is still poorly understood. The differential diagnosis should include the possibility of malignancy for highly suspicious lesions, and proper management guidelines should be established. Surgical resection should be the treatment of choice, and once removed, all surgically excised cysts should undergo pathologic evaluation. As clinicians, it is crucial to stay vigilant and have a low threshold for excision and thorough histological examination of specimens to allow early diagnosis and interventions which can significantly improve patient outcomes. Through the suggested guidelines, we hope to aid in better management and intervention in case of malignant transformation of epidermoid cysts.