Prospective study of Merkel cell polyomavirus and risk of Merkel cell carcinoma Helena Faust 1 , Kristin Andersson 1 , Johanna Ekstr€ om 1 , Maria Hortlund 1 , Trude Eid Robsahm 2 and Joakim Dillner 1,3 1 Department of Medical Microbiology, Ska ˚ne University Hospital, Lund University, Malm€ o, Sweden 2 The Cancer Registry of Norway, Institute of Population-based Cancer Research, Oslo, Norway 3 Departments of Laboratory Medicine, Medical Epidemiology and Biostatistics, Karolinska Institutet and Karolinska Hospital, Stockholm, Sweden Merkel cell carcinoma (MCC) is a rare type of skin cancer that has a characteristically increased incidence among immunosup- pressed subjects. The DNA of Merkel cell polyomavirus (MCV) is regularly found in most MCC tumors. We investigated whether Merkel cell polyomavirus (MCV) infection increases the risk for future MCC. Two large biobank cohorts (Southern Sweden Microbiology Biobank and the Janus Biobank), containing samples from 856,000 healthy donors, were linked to the Cancer Registries in Sweden and Norway to identify cases of MCC occurring up to 30 years after donation of a serum sample. For each of the 22 cases (nine males and 13 females), four matched controls were included. The serum samples were analyzed with an MCV neutralization assay and for IgG antibodies to MCV pseudovirions, using JC polyomavirus and cutaneous human papillomaviruses as control antigens. An increased risk for future MCC was associated both with high levels of MCV antibodies [OR 4.4, 95% CI 1.3–17.4] and with MCV neutralizing activity (OR 5.3, 95% CI 1.3–32.3). In males, MCV seropositivity was not associated to MCC risk, whereas the risk was strongly increased in females, both for high levels of MCV antibodies (OR 7.0, 95% CI 1.6–42.8) and for MCV neutralizing activity (OR 14.3, 95% CI 1.7–677). In conclusion, we found prospective evidence that MCV infection is associated with an increased risk for future MCC, in particular among females. Merkel cell carcinoma (MCC) is an aggressive form of skin cancer, with a disease-specific mortality rate up to 50%. 1 Clo- nally integrated Merkel cell polyomavirus (MCV) has been found in cellular DNA from MCC 2 tumors. MCV DNA is common on human healthy skin 3,4 and MCV-specific anti- body responses are common in the general population. 5–8 MCC patients have higher levels of antibodies to MCV cap- sids than control subjects. 5,9 Antibodies to MCV T antigen oncoproteins appear to follow the tumor burden in MCC patients, 10 and it is therefore not known whether the associa- tion between MCV and MCC is induced by the tumor or by the infection. Prospective studies are considered an essential component of causality inference as they can provide infor- mation on the direction of causality of an association. Recently, an international evaluation classified MCV infection as “probably carcinogenic to humans.” 11 Absence of prospec- tive epidemiological studies was one of the reasons cited for considering the epidemiologic data as insufficient for more definite conclusions. Presence of antibodies to MCV correlates strongly with the presence of the MCV DNA in the skin, both when using a neutralization assay 9 or an MCV pseudovirion binding assay. 12 The antibody assays correlate well with each other 12 and higher levels of antibodies correlate with higher viral load of MCV DNA in the skin. 12,13 Because well-validated serological markers of MCV infection exists, the use of case– control studies nested within biobank cohorts prospectively followed for incident MCC can provide information on whether MCV infection does increase the risk for future MCC. Our objective was to investigate whether MCV infection would be associated with MCC also in a prospective study. Material and Methods Cohorts and study design About 524,000 individuals donated about 1.5 million serum samples to the Southern Sweden Microbiology Biobank (SSMB), from 1969 and onward. 14 The major reasons for donating samples are viral diagnostics, screening of blood donors and screening of pregnant women. 14 Controls and cases were matched by reason for donating sample. Although Key words: viral infections, nonmelanoma skin cancer, serology, prospective case–control study, Merkel cell polyomavirus, Merkel cell carcinoma Abbreviations: HPV: Human Papillomavirus; ICD: International Classification of Diseases; MCC: Merkel cell carcinoma; MCV: Merkel cell polyomavirus; SSMB: Southern Sweden Microbiology Biobank Grant sponsor: European Union FP5 (VIRASKIN); Grant sponsor: Swedish Research Council DOI: 10.1002/ijc.28419 History: Received 1 May 2013; Accepted 9 July 2013; Online 7 Aug 2013 Correspondence to: Joakim Dillner, Karolinska Institute, Department of Medical Epidemiology and Biostatistics, Nobels v€ ag 12, 171 77 Stockholm, Sweden, Tel.: 146-768-871-126, E-mail: Joakim.dillner@ki.se Infectious Causes of Cancer Int. J. Cancer: 134, 844–848 (2014) V C 2013 UICC International Journal of Cancer IJC