MedicalResearch.com Interview with:
Dale P. Sandler, Ph.D.
Chief, Epidemiology Branch
National Institute of Environmental Health Sciences
MedicalResearch.com: What is the background for this study?
Response: Not having children is a well-established risk factor for breast cancer, but most of this evidence comes from studies of postmenopausal women since breast cancer before menopause is relatively uncommon. There is growing evidence that some risk factors differ for premenopausal and postmenopausal breast cancer – for example obesity which increases risk for breast cancer after menopause but appears to be protective before menopause.
There was some evidence that breast cancer risk increased shortly after pregnancy. It was thought that this risk lasted for 5 to ten years. Studies were unable to fully characterize the duration of this increase in risk or evaluate factors such as breast feeding, age at birth, or family history of breast cancer that could modify the relationship between recent pregnancy and breast cancer risk. Breast cancer before menopause or age 55 is relatively rare, and few individual studies are large enough to answer these questions.
To answer these questions, we formed the Breast Cancer Collaborative Group, a pooling project involving 20 prospective cohort studies. We included 890,000 women from 15 of these long-term studies across three continents, including over 18,000 incident breast cancer cases. Continue reading