ESR1 and breast cancer: To date, several genetic loci or single nucleotide polymorphisms (SNPs) have been identified to be associated with percent density using genome-wide association studies (GWAS), including a novel locus on chromosome 12q24 and established breast cancer loci, ZNF365, ESR1, LSP1 and RAD51L1, suggesting shared heritability between PD and breast cancer [6–8].