For instance, PLK1 may act as a tumor suppressor gene that regulates estrogen receptor (ER)-regulated gene transcription in breast cancer [27]; RB1 gene, also a tumor suppressor gene, however, is frequently lost in triple-negative breast cancer [28]; CENPA is a significant prognostic marker for ER-positive patients [29]; and HDAC2 and CHEK2 genes have been significantly correlated to CCDC170 fusion subtype and have been reported to be associated with DDR functioning [30,31], which is also suggestive of the CCDC170 fusion subtype’s relationship with DDR. This evidence concerns the gene CHEK2 and breast cancer.