We propose to use magnetic resonance (MRI) to measure the water content of the breast, which, like mammographic radiodense tissue, reflects the amount of fibroglandular tissue in the breast. The main aim of the proposed study is to examine MRI breast tissue composition in relation to markers of pre-natal, childhood and adolescent growth and development. Specific aims are:

(i) To examine MRI breast tissue composition in young women (aged ~18 years) in relation to markers of foetal, childhood and adolescent growth and development;

(ii) to relate umbilical blood cord plasma levels of sex steroid hormones to MRI breast tissue composition in young women;

(iii) to examine MRI breast tissue composition in young women in relation to concurrent levels of endogenous sex hormones, prolactin, and growth factors

(iv) to compare MRI breast tissue composition in young women to mammographic breast density in their mothers

In the long-run, the proposed study has the potential to form the basis for an investigation into longitudinal changes in breast tissue composition from young adulthood, their determinants, and their implications for breast cancer risk and prevention.