To our knowledge, this is the largest genetic association study in cancer so far. The power of this approach is demonstrated by the fact that we have found evidence, at genome-wide levels of significance, for more than 40 new susceptibility loci, more than doubling the number of susceptibility loci for breast cancer. The effect sizes of the newly identified loci are generally modest (the highest OR was 1.26). However, the very high levels of statistical significance, the lack of heterogeneity among studies, the generally higher effect sizes for familial cases and the fact that most of the excess of significant associations was concentrated among SNPs selected on the basis of an association in the combined breast cancer GWAS all indicate that these are robust associations. Although the majority of the data are from populations of Northern and Western European ancestry, there was little or no evidence of heterogeneity in the OR estimates between studies, indicating that the associations apply broadly to populations of European ancestry. With more than 60 established breast cancer susceptibility loci, it is becoming possible to discern
