Exposure to tobacco smoke at a young age either by smoking or by being around people who smoke may be related to an increased breast cancer risk. Sixteen studies have examined smoking at a young age. These studies compared women who smoked at a young age to women who had never smoked or who were not currently smokers. Most studies reported a small increase in breast cancer risk associated with starting smoking under age 17. Two studies used women who were never passively exposed to tobacco smoke as the comparison group and found about a doubling of breast cancer risk among young smokers; one of the.
