Mammographic density, the proportion of a breast that is made up of radiodense fibroglandular tissue, is a strong marker of breast cancer risk. Breast cancer incidence rates vary more than 6-fold between countries worldwide, but it is not known whether international variations in distributions of mammographic density exist and, if so, what accounts for them.

The International Pooling Project of Mammographic Density will create the first standardized pooled data/imaging resource, which will include women from more than 20 countries worldwide, spanning low- to high-incidence countries. It will be used to describe and account for international variations in mammographic density and investigate to what extent they contribute to international variations in breast cancer incidence rates.