A prerequisite for prevention or early diagnosis of a tumour disease is that environmental and/or genetic risk factors are characterized in order to better define risk groups. The present research proposal focus on common malignant tumours, especially breast cancer and malignant melanoma . By combining risk factor studies on endogenous and exogenous environmental, and genetic risk factors and its interaction, the aim is to better characterize strong determinants of risk. The project also aims at better understanding the mechanisms of disease and for different exposures, such as sun exposure and different hormonal exposures, obtain a global assessment of possible positive and negative health and disease effects. The infrastructure includes large population based cohort and case-control studies, pathological and clinical patient information, biobanks from cancer patients and controls, availability of excellent genomic resources and an extensive network of national and international collaborations. Very often it has been possible to work out from a population based perspective. Both for breast cancer and melanoma the research group has identified important genes or modifiers of dominant predisposing genes as well as environmental or constitutional risk factors. Through an extensive international collaboration gene and gene-environemnt interaction studies are undertaken. The ulitmate goal for the new knowledge is to prevent or early diagnose the malignancy. In hereditary cancer and for some of the hormonal exposures successful results already are seen. The applicant has been involved more than 30 years in epidemiological research of cancer, and published more than 400 publications in international journals and fostered a large number of PhD students.