The one with the "highest risk" cannot be established without a world survey. WE should consider causes then risk factors that exacerbate these causes. Breast cancer has a heritable form, controlled by the gene BRCA1 that is found in both male and female. When BRCA1 and gene p53 is mutated in the same cell, breast cancer develops. With gene p53 mutated, BRCA1 cannot connect with Rap80, a protein that is involved in the repair of damaged genes. BRCA1 can also be damaged by environmental factors like free radicals and their derivatives; these also mutate gene p53. This gene is a switch; it can stop cell division (then uncontrolled growth) in the interphase at two points. I have a Hub on this topic.
Other causes of breast cancer are X-rays. One gets both free radicals and X-rays from the smoke of tobacco that contains polonium 210 and lead 210, both radioactive materials. As they decay, they emit X-rays and generate free radicals. To repeat, the causes of breast cancer are heredity, free radicals and their derivatives, and X-rays.