BRCA1 and cancer: It has been noted that in the presence of heterozygous hereditary mutations in the BRCA1 genes, the likelihood of a secondary inactivating mutation, deletion, or hypermethylation of the promoter increases, and in such cells, there is a violation of DNA repair, which leads to genomic instability, various chromosomal aberrations, and, as a result, an increased risk of developing cancer [3].