Treatment for the first BC is also known to modify subsequent CBC risk and has been studied in combination with specific genetic risk factors; examples include the use of tamoxifen in carriers of pathogenic germline variants (PGVs) in BRCA1 and BRCA2 [17,18,19] and the effects of radiation exposure in combination with pathogenic variants in ATM [20]. This evidence concerns the gene BRCA1 and breast cancer.