Exposure to cigarette smoke linked to postmenopausal breast cancer
Postmenopausal women who smoke may be 16 per cent more likely to develop breast cancer than those who have never smoked, a US study has found.
The research, which is published in the British Medical Journal, also indicates that extensive exposure to secondhand smoke may affect a woman's risk of the disease.
Scientists at West Virginia University and the HealthPartners Research Foundation in Minneapolis carried out a large-scale study to investigate the links between active and passive smoking and breast cancer.
The research team analysed data on almost 80,000 American women, aged 50 to 79 years, who had taken part in the Women's Health Initiative Observational Study between 1993 and 1998.
During the ten-year follow-up period, a total of 3,520 cases of invasive breast cancer were identified among the women taking part.
Analysis revealed that women who smoked had a 16 per cent increased risk of developing breast cancer after the menopause.
The risk was particularly high among women who had smoked for more than 50 years, or who had started smoking during their teens.
Women who used to smoke but had given up by the time of the study had a nine per cent increase in their risk of postmenopausal breast cancer.
This increased risk of breast cancer continued for up to 20 years after an individual stopped smoking.
Worryingly, the study also revealed that non-smoking women who had been exposed to extensive passive smoking - more than ten years' exposure during childhood, 20 years' exposure as an adult at home, or ten years' exposure as an adult at work - had a 32 per cent increase in their risk of breast cancer.
However, the study authors conceded that they had only considered women with the greatest exposure to second-hand smoke, and that further research is needed in this area.
Dr Karen Margolis, one of the study's lead authors from the HealthPartners Research Foundation, said: "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."
Yinka Ebo, senior health information officer at Cancer Research UK, said: "We already know that tobacco can cause over a dozen different cancers, and this study adds to the growing evidence that smoking can raise the risk of breast cancer. Being a non-smoker is still the best way to reduce the risk of cancer. It's never too late to quit and it's better not to start at all."