Exposure to estrogen.  Because the female hormone estrogen stimulates breast cancer growth, exposure to estrogen over long periods of time, without any breaks, can increase the risk of breast cancer.  Some of these risk factors are under your control, such as: taking combined hormone replacement therapy (estrogen and progesterone; HRT) for several years or more, or taking estrogen alone for more than 10 years, being overweight,  regularly drinking alcohol.  Recent oral contraceptive use.  Using oral contraceptives (birth control pills) appears to slightly increase a woman’s risk for breast cancer, but for only a limited period of time.  Women who stopped using oral contraceptives more than 10 years ago do not appear to have any increase breast cancer risk.  Stress and anxiety.  There is no clear proof that stress and anxiety can increase breast cancer risk.  However, anything you can do to reduce your stress can have a major effect on your quality of life: so-called “mindful measures” (such as meditation, yoga, visualization exercises, and prayer).  Some research suggest that these practices can strengthen the immune system.

Source:  NCI  2019