Exposure to high levels of secondhand smoke may increase postmenopausal breast cancer risk

Cumulative exposure to high levels of secondhand smoke during adulthood was associated with an elevated risk for breast cancer, particularly among postmenopausal women.

“The question of whether exposure to sidestream smoke could increase risk of breast cancer is one that is unresolved,” Peggy Reynolds, PhD, MPH, senior research scientist at Northern California Cancer Center in Berkeley, said in a press release.

“While no single epidemiologic study can answer the question, our findings suggest that cumulative high levels of exposure may contribute to breast cancer, adding to the evidence for a variety of other adverse health outcomes,” she said.

Researchers examined data from 57,523 nonsmoking women enrolled in the California Teachers Study. They assessed information about time periods, ages of exposure and settings of exposure, including home, workplace and social.

There were 1,754 women diagnosed with invasive breast cancer. Overall, passive smoking exposure was reported in 86% of women.

The HR for women in the highest exposure category during adulthood (aged 20 years or older) was 1.18 (95% CI, 1.00-1.40). For women in the modest to high exposure category, there was a statistically significant nonlinear dose response.

Among postmenopausal women, the HRs were 1.17 (95% CI, 0.91-1.49) for low lifetime cumulative exposure, 1.19 (95% CI, 0.93-1.53) for medium lifetime exposure and 1.26 (95% CI, 0.99-1.60) for high lifetime exposure.

The risk for breast cancer was slightly increased for women with exposure before a first pregnancy in age- and race-adjusted analysis (HR=1.21; 95% CI, 1.00-1.47) and fully adjusted analysis (HR=1.17; 95% CI, 0.96-1.41).

Reynolds P. Cancer Epidemiol Biomarkers Prev. 2009;doi:10.1158/1055-9965.EPI-09-0936.