What affects a person’s risk of breast cancer? Breast cancer risk factors are like puzzle pieces. We know how some of the puzzle pieces fit together and affect risk. For other risk factors, we are just learning about the role they may play.

Gender is the main factor that affects risk. Women have higher breast cancer rates than men.

Advancing age, the age when a girl gets her first period, the age when a woman stops menstruating, a higher consumption of alcohol, and the use of hormone replacement therapy also affects breast cancer risk. These factors may increase exposure to certain reproductive hormones, such as estrogen and progesterone, which can stimulate breast cells to divide and grow.

A dividing cell is more prone to making mistakes when copying its genetic material, leading to a higher rate of “by chance” or spontaneous mutations. A mutation can also be induced by an environmental chemical. Normally, our cells are very efficient at repairing these damaging mutations. However, a spontaneous or an induced mutation can be made permanent and be passed on to new daughter cells during cell division.