<p id="par0005">The International Consortium on Mammographic Density (ICMD) is a pooling study of individual-level epidemiologic data and mammographic density information.p>
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<p id="par0010">The rationale and methods of ICMD are described.p>
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<p id="par0015">11755 women, from 27 studies in 22 countries are included.p>
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<p id="par0020">The immense heterogeneity in breast cancer risk factors are highlighted.p>