The results of studies “with thorough passive smoking exposure assessment” indicate that passive smoking raises the risk of breast cancer, especially in premenopausal women, to a similar degree as active smoking.

Dr. Kenneth C. Johnson, of the Public Health Agency of Canada, Ottawa, Ontario, examined the association between breast cancer risk and passive and active smoking in an analysis of 19 published studies that met basic quality criteria. The results are published in the International Journal of Cancer.

The investigator calculated the risk of breast cancer in life-long non-smokers with regular exposure to passive smoke, and for women who smoked compared with women who were never regularly exposed to tobacco smoke.

Long-term regular exposure to passive smoking was associated with an overall 27-percent increased risk of breast cancer among women who had never smoked.

“More importantly, among the studies that collected the most complete measures of passive smoking, the observed breast cancer risk was increased by 90 percent,” Johnson said in an interview with Reuters Health. “Studies with less complete second-hand smoke measures only observed an eight-percent increase in risk.”

“The relationship with premenopausal breast cancer risk was stronger - elevated 68 percent with long-term regular passive smoking exposure among life-long non-smokers based on 14 studies,” Dr. Johnson explained. “The premenopausal risk was up 119 percent for the five studies with more complete second-hand smoke measures.”

Compared with women with neither active nor regular passive smoke exposure, those who smoked had a 46-percent increased risk of breast cancer. The risk was raised 108 percent in studies with more complete passive exposure assessment. For studies with less complete passive exposure assessment, the risk was increased by 15 percent.

Johnson noted that tobacco smoke exposure was epidemic in many developed countries for at least the last half century.

“In our Canadian breast-ETS study included in the (analysis), we found that more than 50 percent of women had reported smoking and another 40 percent had had regular long-term exposure to passive smoking, either growing up with parents who smoked, living with a spouse who smoked or working with smokers,” he said.

“Luckily, the landscape is changing rapidly regarding smoking in public places in North America in particular, but there are still many children, spouses, and workers being unnecessarily exposed to tobacco smoke daily,” the investigator stressed. “It is clearly time to redouble efforts to reduce non-smokers’ exposure to second-hand smoke in all environments,” he concluded.

SOURCE: International Journal of Cancer, November 2005.