So, summarizing the materials obtained in this section of the work, devoted to the assessment of the functionality of BC-associated loci and strongly linked polymorphisms, we can note the following: Firstly, the presence of pronounced functional effects (epigenetic modifications, eQTL, and sQTL) of BC-risky SNP rs10454142 PPP1R21 and 10 proxy SNPs in relation to 11 genes, including BC biology, important to organs/cells such as the mammary gland (8 genes), fibroblasts (4 genes), and liver (4 genes), were found. Here, PPP1R21 is linked to breast cancer.