“Breast cancer is the most common cancer to affect women worldwide,” said lead study author Fei Xue, MD, ScD, of the Department of Obstetrics and Gynecology at BWH. “Knowing that tobacco smoke contains potential human breast carcinogens, we wanted to determine whether there was a connection between smoking and breast cancer risk.”
Using data collected from the Nurses’ Health Study, the researchers examined the records of 111,140 women from 1976 to 2006 for active smoking and 36,017 women from 1982 to 2006 for passive, or secondhand, smoking. They found that the development of breast cancer was associated with a higher quantity of current and past smoking, smoking for a longer period of time, younger age at smoking initiation and more pack-years (the number of packs per day and the number of years that quantity was smoked) of smoking. Women who smoked more than 30 pack-years between menarche and menopause had a 28% higher incidence of breast cancer than never smokers.
Smoking before menopause was positively associated with breast cancer risk, though smoking after menopause was shown to potentially be associated with a slightly decreased breast cancer risk. “This difference may suggest an antiestrogenic effect of smoking among postmenopausal women that may further reduce their already low endogenous estrogen levels,” said senior study author Karin B. Michels, ScD, PhD, of the Department of Obstetrics and Gynecology at BWH, noting the many other serious health risks of smoking at any age, including after menopause. Researchers found that passive smoking in childhood or adulthood was not associated with an increase in breast cancer risk.
“Though we did not find an association between light to moderate or passive smoking and breast cancer risk, it is important to highlight the many potential health risks beyond breast cancer that have a proven association with smoking,” said Dr. Xue.