Mother-daughter breast density study points way to earlier cancer risk assessment

(Toronto – April 30, 2009) – A unique mother-daughter study that used magnetic resonance to measure breast density in younger women shows that percent of breast water could be linked to the risk of breast cancer in middle age and older.

The findings, published online today in Lancet Oncology, add another key piece to the puzzle of understanding more about breast density, an inheritable characteristic known to be a cancer risk factor, that could aid in developing prevention methods, says principal investigator Dr. Norman Boyd, a scientist at The Campbell Family Institute for Breast Cancer Research at Princess Margaret Hospital.

Dr. Boyd initially verified breast density (mammographic density, or MD) as a strong risk factor for breast cancer in middle aged and older women in a landmark study published in the New England Journal of Medicine in 2007. Until now, little was known about the development of breast density in early life, or how it relates to a young woman's height, weight and age, and the breast density of their mothers.

The findings of the current study indicate that risk assessment using less harmful techniques such as magnetic resonance imaging (MRI) instead of X-ray should start much earlier in life.

Says Dr. Boyd: "It is known that the breast is most susceptible to the effects of carcinogens at early ages. Our findings suggest that differences in breast tissue composition in early life may be a potential mechanism for this increased susceptibility. By identifying the environmental and genetic factors that influence breast tissue composition in early life we may be able to develop safe and effective methods of prevention."

In this study, between 2003-2006, the researchers recruited 400 mother-daughter pairs and used MRI to examine breast tissue in daughters, aged 15-30-years, and a random sample of 100 of the mothers. In the young women, MRI was used to measure breast water concentration to avoid exposure to radiation from mammograms. Blood was obtained from each woman within 10 days of the start of the most recent menstrual period. Mothers underwent mammography and a random sample of 100 also consented to have a breast MRI.

Results show that percent breast water variation is higher in 15-19 year olds than in 20-30 year olds, and decreases with age, as backed by analysis of the 100 mother-daughter pairs who both had MRI.

The researchers found that in mothers, percent breast water as measured by MRI was strongly linked with percentage of mammographic density. Percent breast water in daughters (median 45%) was significantly higher than in mothers (28%), and decreases as their age and weight increases, but increases with increasing height. It was also linked to increasing MD in their mothers. Weight, height, and the mothers MD are known risk factors for breast cancer.

Higher blood growth hormone concentrations were also linked to higher percent breast water. Results showed that each 5cm difference in height in daughters was associated with 3% increase in percent breast water, which suggests a mechanism by which growth might affect the risk of cancer.

This research was supported by the Canadian Breast Cancer Research Alliance, with special funding support from the Canadian Breast Cancer Foundation – Ontario Region.

The Campbell Family Institute for Breast Cancer Research at Princess Margaret Hospital brings together an elite team of cancer researchers, scientists, clinicians and staff dedicated to the ultimate goal of conquering breast cancer by leveraging basic, translational and clinical research into dramatic breast cancer breakthroughs. www.campbellfamilyinstitute.com

Princess Margaret Hospital and its research arm Ontario Cancer Institute -- which includes The Campbell Family Cancer Research Institute and The Campbell Family Institute for Breast Cancer Research -- have achieved an international reputation as global leaders in the fight against cancer. Princess Margaret Hospital is a member of University Health Network, which also includes Toronto General Hospital and Toronto Western Hospital. All three are research hospitals affiliated with the University of Toronto. www.uhn.on.ca

The Canadian Breast Cancer Research Alliance was established in 1993 and is the primary granting agency for breast cancer research in Canada. It is a unique collaboration of organizations from the public, private and non-profit sectors combining resources to more effectively support and promote breast cancer research of the highest quality in Canada.

CBCRA members are the Avon Flame Foundation, the Canadian Breast Cancer Foundation, the Canadian Breast Cancer Network, the Canadian Cancer Society, the Canadian Institutes of Health Research, Health Canada and the Public Health Agency of Canada. www.breast.cancer.ca

For more information or to arrange an interview, please contact: Jane Finlayson, Public Affairs, (416) 946-2846 jane.finlayson@uhn.on.ca