Basal cell carcinoma arising from an epidermal cyst: when a cyst is not a cyst.

Malignant degeneration within epidermal cysts is very rare. However, these lesions may not be recognised clinically, and histological examination plays an important role in arriving at a correct diagnosis. Hence, we believe that benign-looking cystic lesions with a history of progressive growth should be surgically excised and submitted for histopathological assessment.