Several factors are thought to be associated with the occurrence and development of bilateral breast cancer, such as early age at diagnosis, histology, family history, and especially the presence of germline deleterious variants that include BRCA1/2, PALB2, CDH1, and CHEK2. Studies have reported that the prognosis of BBC patients is similar or worse than unilateral breast cancer (UBC) patients [4–7]. The gene discussed is CHEK2; the disease is breast cancer.