look up BRCA 1,2 genes. They cause breast and ovarian cancers for women and men under 40. These are defects in DNA that pre-dispose several types of cancer, because the body lose the ability to repair problematic gene copies. BRCA is a gene that does the repair. These problematic copies lead to cancer. Celebrity Angelina Jolie had surgery to remove breasts and ovaries to prevent cancers from BRCA1,2 genes.