The Japanese-German Workshops "Molecular and Cellular Aspects of Carcinogenesis," held biennially since 1987, have been organized traditionally at the University of Essen Medical School and West German Cancer Center Essen in Germany. This 9th Workshop was held on September 18-20, 2003. It was generously supported by the Cancer Research Program of the Ministry of Education, Culture, Sports, Science and Technology and the International Cooperation Program for the 2nd Term Comprehensive 10-Year Strategy for Cancer Control of the Ministry of Health, Labour and Welfare on the Japanese side, and by the Deutsche Forschungsgemeinschaft (DFG) on the German side. Additional support from many other sponsors in Germany and Japan is gratefully acknowledged. The Workshop participants are listed at the end of this Report.