One in nine women in the UK have a lifetime risk of breast cancer, with a similar proportion for other developed countries worldwide. Previous research investigating a possible association between smoking and breast cancer has been inconclusive. Using data in a Canadian population in British Columbia, Pierre Band and colleagues from British Columbia Cancer Agency, Vancouver, Canada, compared women with and without breast cancer in terms of their history of smoking, controlling for risk factors known to be associated with breast cancer (such as hormone replacement therapy). Data were analysed separately for premenopausal and postmenopausal women.

Over 600 premenopausal and 1400 postmenopausal women with and without breast cancer (women without breast cancer were the control group) replied to an initial survey targeted at around 1500 women with breast cancer and a further 1500 age-matched controls. Women who started smoking within five years of menarche (onset of menstruation) were around 1.7 times (70%) more likely to develop breast cancer than non-smokers.

Pierre Band comments: "These results-which suggest that human breast tissue is most sensitive to environmental carcinogens during periods of rapid cell proliferation when differentiation is incomplete (puberty)-add epidemiological evidence to experimental studies, relating susceptibility to carcinogenesis to the biology of breast development. Our observations reinforce the importance of smoking prevention, especially in early adolescence." He adds: "British Columbian women have a premenopausal breast cancer risk of 1 in 55. An increased risk off 70% would lead to an additional 1000 premenopausal breast cancer cases out of 100 000 teenage smokers
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Contact: Richard Lane
richard.lane@lancet.com
44-207-424-4949
Lancet
3-Oct-2002