1. Department of Laboratory Medicine; Karolinska Institutet; Stockholm SE-141 86 Sweden
2. Department of Clinical Sciences; Lund University; Malmö Sweden
3. National Institute for Health and Welfare; Oulu Finland
4. Abteilung Tumorvirus-Charakterisierung, Deutsches Krebsforschungszentrum; Heidelberg 69120 Germany
5. Department of Medical Epidemiology & Biostatistics; Karolinska Institutet; Stockholm SE-171 77 Sweden