Usefulness of ulceration and hyperkeratosis as clinical predictors of Merkel cell polyomavirus-negative and combined Merkel cell carcinoma: A retrospective study

Merkel cell carcinoma is a rare neuroendocrine carcinoma of the skin that is associated with Merkel cell polyomavirus (MCPyV). The clinical appearance and demographic characteristics of this tumor have been described using the mnemonic AEIOU: asymptomatic, expanding rapidly, immune suppression, older than 50 years, and ultraviolet-exposed fair skin. In addition, MCC can be categorized based on morphology as pure MCC or combined MCC that exhibits neuroendocrine and other phenotypic elements. There is limited information regarding the clinical characteristics and prognosis of combined MCC. This retrospective study aimed to identify factors, such as ulceration or hyperkeratosis, that could predict MCPyV status and morphological variants. Twenty patients with MCC were divided into groups based on MCPyV status and morphology: MCPyV-positive or MCPyV-negative MCC and pure or combined MCC. The patients' MCPyV status was immunohistochemically determined using the CM2B4 antibody to the MCPyV large T-antigen. The patients' clinicopathological characteristics were evaluated to identify predictors of MCPyV-negative MCC and combined MCC. The presence of ulceration/hyperkeratosis predicted the presence of MCPyV-negative MCC (80% of cases) and combined MCC (50% of cases). None of the 10 patients with MCPyV-positive MCC had ulceration/hyperkeratosis. The clinical presence of ulceration/hyperkeratosis may help guide the diagnosis of MCPyV-negative MCC and combined MCC.