What are the non-genetic causes of breast cancer for the women?

Our Environment: Most cases of breast cancer in the US are unrelated to genetics and are believed to be due to our environment. Breast cancer is a disease of the modern world and is much less common in developing nations. Whether it is a byproduct of what we breathe and/or what we eat, the exact causes are unclear. However, we do see cancer more commonly in women with early menarche, late menopause, etc.

Multifactorial: The majority of women who develop breast cancer have no family history of breast cancer. Risk factors include estrogen therapy, obesity, early menarche, late menopause, and sometimes just plain bad luck.