Metastatic Merkel cell carcinoma of the oral cavity in a human immunodeficiency virus-positive patient and the detection of Merkel cell polyomavirus.

The etiology of Merkel cell carcinoma (MCC) was recently linked to a newly identified human virus, the Merkel cell polyomavirus (MCPyV). The discovery that MCPyV plays an important role in the tumorigenesis of >80% of MCCs provides an explanation for the increased incidence of this rare malignancy in human immunodeficiency virus (HIV)-positive and immunocompromised patients. We report an unusual metastasis of MCC to the mandibular gingiva of an HIV-positive patient. In addition to routine hematoxylin-eosin and immunohistochemical studies, we also performed a molecular biologic analysis to look for the presence of MCPyV in this case. We detected evidence of the MCPyV genome in this lesion similar to what has been observed for MCCs reported in other immunocompromised patients. These results stress the importance of combining morphologic and molecular biologic analyses in the evaluation of MCC, because confirmation of viral etiology would likely affect the choice of treatment and prognosis when specific antiviral therapy becomes available for this aggressive tumor.