Breast cancer risk factors illuminated in studies

A large, prospective study from the Mary Babb Randolph Cancer Center at West Virginia University in Morgantown compared female ever-smokers with never-smokers and found that ever smoking cigarettes increases the risk for invasive breast cancer by 9% and current smoking increases the risk 16%.

The researchers included almost 80,000 postmenopausal women between the ages of 50 and 79 years participating in the Women's Health Initiative Observational Study and followed them for 10 years. They found the highest risk among current smokers with the highest intensity and duration of smoking and also among women who began smoking during their teen years or before their first full-term pregnancy. Among former smokers, an increased risk persisted for up to 20 years after they quit smoking.

Researchers also found a 32% increased risk associated with extensive exposure to second-hand smoke compared with those unexposed, but they stipulated that further research is needed in this area.

Researchers at the Fred Hutchinson Cancer Center in Seattle, Washington, found that women in the highest versus the lowest body mass index quartile had 35% and 39% higher risks for triple-negative and ER+ breast cancer, respectively (1.35; 95% CI, 0.92-1.99 and 1.39; 95% CI, 1.22-1.58). Waist and hip circumference also were positively associated with the risk for ER+ breast cancer (P _trend =0.01 for both measures), but were unassociated with the risk for triple-negative disease.

Compared with women who reported no physical activity, those in the highest tertile for recreational exercise had similarly low risks for triple-negative and ER+ breast cancers (HR=0.77; 95% CI, 0.51-1.13 and HR=0.85; 95% CI, 0.74-0.98, respectively).

Luo J, Margolis KL, Wactawski-Wende J, et al. Association of active and passive smoking with risk of breast cancer among postmenopausal women: a prospective cohort study. BMJ. 2011;342:d1016.

Phipps AI, Chlebowski RT, Prentice R, et al. Body size, physical activity, and risk of triple-negative and estrogen receptor-positive breast cancer. Cancer Epidemiol Biomarkers Prev. 2011;20(3):454-463.