Women who breathed a lot of secondhand smoke during their lifetime but who never smoked appear to be at greater risk of developing breast cancer later, according to City of Hope researchers and colleagues.
The study — one of the largest ever on passive smoking and breast cancer risk — appeared in the December 2009 issue of Cancer Epidemiology, Biomarkers & Prevention. Leslie Bernstein, Ph.D., director of the Division of Cancer Etiology, was the study’s senior author; Katherine Henderson, Ph.D., assistant research scientist in the division, was a co-author.
|Leslie Bernstein (Photo by Walter Urie)|
“Research now shows that women who started smoking as teenagers, during a critical window of breast development, have greater breast cancer risk than nonsmoking women,” said Bernstein, “but links between exposure to secondhand smoking and breast cancer risk have been tenuous.
“We need to clarify this issue, particularly since breast cancer is the leading cancer among women.”
The team turned to the California Teachers Study for more answers.
The California Teachers Study follows the medical history, lifestyle and health of nearly 133,500 female teachers and administrators who have worked in the California public school system.
In 1995, researchers asked women about exposure to cigarette smoke in their homes over their lifetimes — smoking by parents, roommates or a spouse. Two years later, they gathered information on secondhand smoke exposure in the workplace, in social situations and at other places outside the home, asking about exposures at different periods during their life. Scientists also asked about the intensity of the smoke to which women were exposed and the duration of their exposures.
Restricting their study to the 66 percent of women who were lifetime nonsmokers and who had no history of breast cancer in 1997, the researchers followed more than 57,000 women for more 10 years. Of these participants, 1,754 went on to develop new, invasive breast cancers.
The researchers found that never-smoking postmenopausal women with high intensities of secondhand smoke exposure after age 20 had greater risk of breast cancer than similar women with little exposure. Among these women, those exposed to the most secondhand smoke for the longest time had a 26 percent higher risk of breast cancer than women with little or no exposure to secondhand smoke.
The California Teachers Study provides some of the most extensive data and is one of the largest studies ever conducted on secondhand smoke and breast cancer risk.
Although federal and international agencies have classified secondhand smoke as a carcinogen, researchers are unsure how it may specifically increase breast cancer risk or whether it may increase breast cancer risk among some women more than others.
The study’s lead author was Peggy Reynolds, Ph.D., of the Northern California Cancer Center (NCCC) and Stanford University, and included additional scientists from NCCC, as well as University of California, Irvine.
The National Cancer Institute, California’s Tobacco-Related Research Program and the California Breast Cancer Research Fund supported the study. Cancer Epidemiology, Biomarkers & Prevention is a journal of the American Association of Cancer Research.