Abstract

We present the case of a 74-year-old female with a past medical history significant for melanoma, two squamous cell carcinomas, and basal cell carcinoma, who presented to clinic for an annual skin cancer evaluation. On examination, the patient had a new 1-cm crusty nodule involving the right dorsal heel. The differential diagnosis was callus versus squamous cell carcinoma versus melanoma. Shave biopsy was performed, and histopathologic evaluation revealed an endophytic atypical and inflamed squamous proliferation. A staged surgical excision was performed, which included a debulk of the gross tumor. The debulked tissue showed an inflamed squamous proliferation. There was a hyperplastic epidermis with a complex arrangement of lobules extending into the dermis, and small cysts containing neutrophils were noted within these lobules. Reactive cytologic changes, as well as many eosinophils and neutrophils, were also seen. On some levels, a chronic granulomatous inflammatory infiltrate was noted in association with gout crystals, which were present in direct juxtaposition to the hyperplastic epidermis. P63 stain showed only rare small strands of keratinocytes in the dermis, and CK 5/6 stain demonstrated small strands of keratinaceous cells with only a minority appearing to represent infiltrative strands of viable keratinocytes. In this clinical setting and given the patient's history of gouty arthritis, the findings were attributed to reactive changes caused by transepidermal elimination of gout crystals. This case exemplifies gout clinically and histologically mimicking SCC in a patient with an extensive skin cancer history. This case should serve as a reminder for dermatologists and dermatopathologists to take into consideration a patient's medical history and to consider transepidermal elimination from a tophus in the differential diagnosis of an atypical squamous proliferation, especially when the biopsied lesion appears at a location typical for a gouty tophus.

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