CK20/CK7 double‐negative Merkel cell carcinoma in situ: A case report.

An 83‐year‐old male with a history of both melanoma and non‐melanoma skin cancers presented with a light pink non‐ulcerated slightly raised 0.6 × 0.5‐cm papule on his left lower extremity. Biopsy specimen revealed a proliferation of intraepidermal round blue cells. On immunohistochemical staining, CD56, chromogranin, and pancytokeratin were faintly positive within the lesional population, while synaptophysin was strongly positive. CD45, CK5/6, CK7, CK20, Melan‐A, SOX10, and TTF‐1 stains were negative. There was no dermal component identified. A Merkel cell polyomavirus stain was negative. Distant metastases and other in situ pathologies were excluded and a diagnosis of Merkel cell carcinoma in situ (MMCIS) was made. The majority of MCCIS lesions reported in the literature have been discovered amongst other non‐melanoma neoplasms. Our findings of an MCCIS with purely intraepidermal involvements without the association with another squamous cell neoplasm is rare finding. [ABSTRACT FROM AUTHOR]

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