What are risk factors for developing breast cancer?

Female sex (female to male > 100:1)
Age more than 40 years
Family history of breast cancer, especially premenopausal or bilateral breast cancer in a first-degree relative (mother or sister) Previous history of breast cancer, LCIS, or atypia
Early menarche and late menopause
Nulliparity or age more than 35 years at first full-term pregnancy
Obesity
BRCA 1 or 2 carriers (BRCA 1 and 2 are genetic mutations that put carriers at high risk for developing breast cancer)
Prior radiation therapy (e.g., Hodgkin s lymphoma as a child)
Ashkenazi Jewish descent