Smoking raises breast cancer risk in postmenopausal women

A new research has found that postmenopausal women who smoke or used to smoke have up to a 16% higher risk of developing breast cancer compared to women who have never smoked.

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.

The researchers, led by Dr Juhua Luo from West Virginia University and Dr Karen Margolis from the HealthPartners Research Foundation in Minneapolis, used data from the 1993-98 Women's Health Initiative Observational study to determine links between smoking, passive smoking and breast cancer.

They analysed data for almost 80,000 women, aged between 50 and 79 years, across 40 clinical centres in the United States. In total, 3,250 cases of invasive breast cancer were identified by the researchers during ten years of follow-up.

The participants were asked a range of questions about their smoking status, for example whether they had ever smoked or were former or current smokers. Current or former smokers were asked the age at which they started smoking and the number of cigarettes smoked a day. Former smokers were asked the age at which they quit.

Questions on passive smoking related to whether the participants lived in smoking households as children and/or as adults, and whether they had worked in smoking environments.

The results show that smokers have a 16% increased risk of developing breast cancer after the menopause. The increased risk for former smokers is 9%. The highest breast cancer risk was found among women who had smoked for over 50 years or more compared with lifetime non-smokers. Women who started smoking as teenagers were also at particularly high risk. An increased risk of breast cancer continued for up to 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 over 10 years' exposure in childhood; over 20 years' exposure as an adult at home and over 10 years' exposure as an adult at work; had a 32% excess risk of breast cancer.

The research has been published on bmj.com.