The Pharmaceutical Journal
Vol 269 No 7219 p518
12 October 2002

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The Lancet (www.thelancet.com)
Cancer Research UK (www.cancerresearchuk.org)

Breast cancer risk higher for teenage smokers

Women who smoke in their teens increase their risk of developing breast cancer later in life, Canadian researchers suggest.

They investigated smoking and medical history in over 1,000 women with breast cancer and a similar number who did not have the disease. They found that pre-menopausal, parous women who had started smoking within five years of the onset of menstruation, were 70 per cent more likely to develop breast cancer, compared with parous non-smokers (P=0.01). In addition, nulliparous, premenopausal women who smoked more than 20 cigarettes a day were seven times more at risk of breast cancer than nulliparous, premenopausal non-smokers (P=0.009). The research is published in The Lancet (2002;360:1044).

However, cigarette smoking was not associated with an increased risk of breast cancer in post-menopausal women. Indeed, those whose body mass index had increased to more than 21 after they were 18 years old, actually halved their risk of breast cancer if they had started smoking after their first pregnancy (P=0.02).

The researchers say their results suggest that human breast tissue is most sensitive to carcinogens during periods of rapid cell proliferation when differentiation is incomplete, as in puberty, or when complete differentiation is never achieved, as occurs in nulliparous women.

Lead author, Dr Pierre Band, of the University of Ottawa, said: "These results 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."

Dr Stephen Duffy, of Cancer Research UK's mathematics, statistics and epidemiology department, commented: "This study suggests an increased risk of breast cancer for women who smoke in their teens and a decreased risk of the disease for women who take up smoking later in life, after their first pregnancy. Both of these could be chance findings since the study is relatively small. The picture remains confusing and we need further research to clarify the effects of smoking on breast cancer risk."