A case of squamous cell carcinoma arising in a giant porokeratosis previously diagnosed as psoriasis.

Porokeratosis (PK) is a disorder of keratinization with a clinical presentation of an atrophic center surrounded by a hyperkeratotic border. Lesions of porokeratosis carry a risk of malignant transformation with giant porokeratosis (GPK) being a high-risk variant. We report a case in which a single, large, erythematous, scaly plaque in an immunocompromised patient showed initial histopathological features consistent with psoriasis and subsequent histological features consistent with GPK.