Recurrent squamous cell carcinoma arising within a linear porokeratosis

Here we report a case of linear porokeratosis with recurrent malignant degeneration to squamous cell carcinoma (SCC) recurring six years after excision of initial SCC. A 79-year-old woman presented with a friable tumor located within a longstanding lesion on her posterior thigh. Six years prior, she was diagnosed with SCC arising within the same lesion, which had been surgically excised with negative margins. Physical examination revealed a 3.5 x 2.7 cm friable tumor on the left proximal posterior thigh.The tumor was located within a hyperpigmented and erythematous scaly linear plaque within a line of Blaschko, extending from the left buttock to the left distal posterior thigh.Two 4 mm punch biopsies were performed: one of the erythematous plaque on the left buttock and one from the friable tumor on the left posteromedial thigh. Histology from the left buttock revealed a cornoid lamella consistent with porokeratosis and the left posteromedial thigh revealed SCC.The patient underwent Mohs micrographic surgery with negative margins, followed by a linear repair. Porokeratosis is a disorder of epidermal keratinization that has been associated with malignant degeneration, although such cases are rare.The risk of recurrence of SCC arising within a porokeratosis is unknown.This case emphasizes the importance of ongoing monitoring for malignant degeneration within these lesions.