Merkel cell polyomavirus is present in common warts and carcinoma in situ of the skin.

Polyomaviruses have been linked to diseases of immunosuppressed patients. We sought to determine the prevalence of Merkel cell polyomavirus in benign epithelial skin neoplasms and nonmelanoma skin cancer of immunosuppressed renal transplant recipients and long-term dialysis patients. Merkel cell polyomavirus DNA was detected by polymerase chain reaction (PCR) in 2 (10%) of 20 patients, in carcinomas in situ (Bowen's disease). In one of our patients with Merkel cell polyomavirus-positive carcinoma in situ, 9 (39.1%) of 23 skin lesions at various anatomical locations tested positive for Merkel cell polyomavirus sequences by PCR, including all of his common warts (4/4), half of his carcinoma in situ lesions (3/6), and 2 of his 3 seborrheic keratoses. In a second cohort of immunosuppressed renal transplant recipients, Merkel cell polyomavirus DNA was found in 1 (6.3%) of 16 common warts and in 2 (9.5%) of 21 carcinomas in situ. In immunocompetent individuals, Merkel cell polyomavirus DNA was found in 2 (6.7%) of 30 common warts and in 2 (8.3%) of 24 carcinomas in situ. DNA of other human polyomaviruses was not detected in any of the investigated skin neoplasms. We conclude that common warts and carcinomas in situ can be positive for Merkel cell polyomavirus in immunosuppressed as well as immunocompetent individuals. Remarkably, some of the Merkel cell polyomavirus-positive common warts did not contain human papillomavirus. Furthermore, Merkel cell polyomavirus can be found in various skin neoplasms of the same individual.