Breast Density Study
Study Code:BD
Sample:Selected from Endometriosis Study
Start Date:Feb.2005
Status:In progress
Contact:Anjali Henders
More Info:QIMR only

Rationale for the Project

Breast cancer is a major cause of early death in Australian women. Breast 'density', a characteristic of women's breasts that can be measured by a mammogram, has been shown by a number of large studies to be a major risk factor for breast cancer. It is a characteristic that can not be measured by breast examination, but is very well measured by a breast scan. Although breast density decreases with age and after menopause, there is a large difference in breast density across women of the same age. Identifying the reasons why women of the same age differ so much in breast density will lead to a better understanding of the cause of breast cancer and have implications for prevention. Professor John Hopper and colleges have conducted a large twin study, in collaboration with Dr Norman Boyd in Toronto, Canada, that has shown that most of this large variation in breast density could be due to as yet undiscovered genetic factors. The genes involved are not BRCA1 and BRCA2, the currently known 'breast cancer susceptibility' genes. They have also found that lifestyle factors, such as number of children, also influences breast density. In this new large study of twins and sister pairs, we shall test whether specific 'hormone' genes, such as estrogen and progesterone, explain part of the genetic effects. We will also study more closely the effects of environmental and lifestyle factors on breast density, especially how their effects interact with those of any genetic factors we identify, by comparing twins and sisters of the same or similar age. By studying women who have had endometriosis, we will be able to find out if their small increased risk of breast cancer is reflected in their breast density. By collecting a blood sample from all participants we will build a large resource that will be used for future genetic studies, trying to discover new genes that influence breast density, and by implication, risk of breast cancer.

Scientific Aims of the Project

The research questions we wish to address are:

1. that percent mammographic density (PMD) tracks strongly with time in an individual across the age range 40 to 70 years

2. that specific variants in estrogen metabolism genes are associated with PMD

3. that number of live births associated with PMD after menopause, and the effect size increases with age; that smoking reduces PMD before menopause but not after menopause

4. that the effects of measured body and lifestyle factors on PMD may differ according to the woman's genotype for one or more estrogen metabolizing genes.