Breast cancer linked to passive smoking

In addition to smoking, exposure to second-hand tobacco smoke as a child or adult appears to increase a woman’s risk of breast cancer, according to a new study published online March 1 in the British Medical Journal.

The prospective cohort study included 79,990 women between 50 and 79 years of age enrolled in the Women’s Health Initiative Observational Study at 40 medical centers in the United States between 1993 and 1998. Analysis of the data showed that women who had never smoked but had lived or worked with smokers for the longest periods-10 years or longer during childhood, 20 years or longer as an adult at home, and 10 years or longer as an adult at work-had an increased cancer risk of 32% compared with never-exposed women.

Women exposed to lesser amounts of passive smoke didn’t show the same risk. The study also found a 16% increased risk of postmenopausal breast cancer for active smokers and a 9% increase in risk for ex-smokers that continued for as long as 20 years after smoking cessation.

“It seems unlikely that this could be explained by bias or confounding for several reasons,” the authors write, noting that the study was prospective in nature, adjusted for all known or suspected confounders for breast cancer, and included data on 3 major aspects of lifetime exposure: childhood, adult residential, and occupational. This enabled the researchers to examine a reference group that hadn’t been exposed to either active or passive smoking. The results remained similar after exclusion of the first 2 years of follow-up.

The researchers call the findings “suggestive” and call for more research to confirm them. They write that that the findings “highlight the need for interventions to prevent initiation of smoking, especially at an early age, and to encourage smoking cessation at all ages.”