dr. ganz: and again, if we understand what the risk factor is or the environmental hazard or what the exposure is that leads to a specific mutation, then we can begin to link interventions in terms of reducing the risk of cancer. successive genetic changes must take place for a normal cell to change into a cancer cell. that's why the chances of developing cancer increase with age and with exposure to cancer causing substances, or carcinogens. harold varmus: obviously, environment also contributes to function and disease but knowing what genes are inherited by any organism is essential to a full understanding of how they operate and how they misfunction when disease occurs. only five to ten percent of all cancers are thought to be inherited. for instance, women with mothers or sisters who have breast cancer are at increased risk for developing the disease. i'd get it very early, and be very treatable... i wasn't surprised because both my mother and my grandmother had-- my maternal grandmother,