Squamous Cell Carcinoma with Pseudo-glandular Features Arising in an Epidermal Cyst: A Diagnostic Pitfall

Introduction: Epidermal cysts are benign lesions that develop at various sites on the body. They are usually present on face, trunk, scalp, and back regions. Transformation of a benign epidermal cyst to malignant cyst is rare. The likelihood of an epidermal cyst transforming into squamous cell carcinoma is between 0.011% and 0.045%. Case Report: A 55-year-old female presented with swelling in the intergluteal cleft region that persisted for four years, with a sudden increase in size and a discharging sinus for the last two months. A clinical diagnosis of infected dermoid cyst was made and surgical excision was done. The specimen was subjected to histopathological analysis. Grossly noted, a partially skin-covered, globular, grey-white cystic structure measuring 12x7 cm. On microscopy, a diagnosis of Squamous Cell Carcinoma with a Pseudo-Glandular Pattern originating from an epidermal cyst was established. Immunohistochemical analysis ruled out glandular differentiation by showing negativity for markers CEA and CK7. Discussion: Epidermal cysts represent the most prevalent non-neoplastic cystic lesions encountered on the body. However, the occurrence of malignant transformation in these cysts is exceedingly rare, with only a limited number of cases documented in the literature. Clinicians should consider the possibility of malignant change in instances of longstanding cysts or when there are notable alterations in size, the presence of pain, ulceration, or discharge.