The female hormone estrogen is “fuel” for about 80% of breast cancers in women who’ve gone through menopause. 

“Menopause itself doesn’t boost the risk for breast cancer, but growing older does,” says breast medical oncologist Rachel Layman, M.D. “The longer a woman’s body has accumulated estrogen during her lifetime, the greater her risk will be.”

Drugs called aromatase inhibitors can stop the body from making estrogen...