Postmenopausal women who smoke or used to smoke have as much as a 16% higher risk of developing breast cancer compared to women who have never smoked, according to research published at bmj.com.
The study also says that women, who have had extensive exposure to passive smoking, either as children or in adulthood, may also have an excess risk of developing breast cancer.
While some previous studies have indicated that smoking increases the risk of breast cancer, the theory that passive smoking is also a risk factor, remains controversial.
The researchers, led by Juhua Luo, PhD, from West Virginia University and Karen Margolis, MD, from the HealthPartners Research Foundation in Minneapolis, decided to carry out a large scale study following participants over a long period of time to investigate the issue further.
“Our findings highlight the need for interventions to prevent initiation of smoking, especially at an early age, and to encourage smoking cessation at all ages,” Margolis stated in a press release.
The research team used data from the 1993-98 Women’s Health Initiative Observational study to determine links between smoking, passive smoking and breast cancer.
They analyzed data for almost 80,000 women, 50 years of age to 79 years of age, across 40 clinical centers in the United States. In total, 3,250 cases of invasive breast cancer were identified by the researchers during 10 years of follow-up.
The participants were asked a range of questions about their smoking status.
The results show that smokers have a 16% increased risk of developing breast cancer after menopause. The increased risk for former smokers is 9%. The highest breast cancer risk was found among women who had smoked for more than 50 years. Women who started smoking as teenagers were also at particularly high risk. An increased risk of breast cancer continued for as many as 20 years after an individual stopped smoking.
The findings also reveal that among non-smoking women, those who had been exposed to extensive passive smoking, for example more than 10 years’ exposure in childhood; more than 20 years’ exposure as an adult at home and more than 10 years’ exposure as an adult at work; had a 32% excess risk of breast cancer.
The authors stress, however, that their analysis of the link between breast cancer and secondhand smoke was restricted to the most extensive passive smoking category and therefore more research is needed to confirm these findings.