Dr. Juhua Luo of West Virginia University and Dr. Karen Margolis of the HealthPartners Research Foundation in Minneapolis say postmenopausal women who smoke have up to a 16 percent higher risk of developing breast cancer compared with women who have never smoked. The increased risk for former smokers is 9 percent, Luo says.
The research team used data from the 1993-1998 Women's Health Initiative Observational study to determine links between smoking, passive smoking and breast cancer that involved almost 80,000 women, ages 50-79, from 40 U.S. clinics.
In total, 3,250 cases of invasive breast cancer were identified during the 10-year, follow-up period.
The study, published in the British Medical Journal, found the highest breast cancer risk was among women who had smoked for more than 50 years or more compared with lifetime non-smokers. In addition, women who took up smoking as teens were at particularly high risk.
Among non-smoking women, women who had been exposed to extensive secondhand smoke -- such as more than 10 years' exposure in childhood, more than 20 years' exposure as an adult at home or more than 10 years' exposure as an adult at work had a 32 percent increased risk of breast cancer.
The study authors say the link between breast cancer and secondhand smoke was restricted to the most extensive passive smoking category and more research is needed to confirm these findings.