ABSTRACT: THE SEARCH FOR INFECTIOUS AGENTS LINKED TO HUMAN CANCERSWe would like to present the abstract of our keynote speaker, the Nobel prize laureate – Harald zur Hausen – who is currently the head of a Division at the Heidelberg Cancer Research Center. During the past 5 decades a number of infectious agents have been linked to specific human cancers. These include viruses (e.g. Epstein-Barr Virus, Human Herpesvirus type 8, Hepatitis B Virus, Hepatitis C Virus, specific human papillomavirus types, T-lymphotropic retrovirus, human immunodeficiency virus, Merkel-cell polyomavirus) as well as bacteria (Helicobacter pylori) and parasitic infections (Schistosoma hematobium, Opisthorchis viverinni). All together, they account for approximately 21 % of the global cancer incidence with wide geographic variations. The identification of these agents had major impact for the development of novel strategies for cancer prevention. We analyzed the question whether it is worthwhile to study additional human cancers linked to these infections. Initially this was based on epidemiological observations by correlating incidence pattern with specific nutritional habits. This resulted in the suggestion the consumption of beef and dairy products of Eurasian cattle significantly contributes to the risk for colon, breast and prostate cancers. Subsequently we isolated and sequenced a large number of small circular single-stranded DNA from sera and dairy products of dairy cows, named bovine meat and milk factors (BMMF) Those which have been tested by now are genetically active in human cells and replicate in specific human cell lines. A high percentage of healthy humans develop antibodies against the major protein (rep) of one subgroup. Four of these molecules have been isolated from materials of patients with multiple sclerosis. Presently, experiments are being conducted to study their role in malignant tumors and in neurodegenerative diseases.