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a) and c) right breast cancer; b) and d) left breast cancer. a-b) hematoxylin and eosin staining ×100; b-d) p53 staining x100.Radiation exposure in LFSLFS-related breast cancer treatment strategies, such as radiation, surgery and drug therapy, are listed in Table 2 according to consensus recommen-dations12). The TP53 gene is the most important tumor suppressor gene in preventing cancer devel-opment. It plays an important role in cell cycle regulation and apoptosis by providing cells with the ability to respond to and repair DNA damage after cellular stress and by triggering multiple downstream repair pathways. Therefore, radiation exposure, which increases the risk of developing a second cancer, should be avoided if there are other options in LFS because DNA damage cannot be repaired. In the present case, LFS was not suspected at the time of the initial breast cancer, and treat-ment and surveillance with RTx and X-rays were performed. It is not easy for a non-geneticist to suspect a hereditary tumor, other than hereditary breast-ovarian cancer syndrome (HBOC). However, it may be necessary to suspect the possibility of a background hereditary tumor related to breast into account the advantages and disadvantages.DiscussionCharacteristics of LFS-related breast cancerBreast cancer is the most common LFS-related tumor, accounting for 27% to 31% of all reported LFS tumors6). LFS-related breast cancer is charac-terized by a median age as young as 33 years, and almost all cases occur before menopause. Among younger breast cancer patients under 30 years, germline TP53 variants were detected in about 4%-8% of cases (without germline BRCA1/2 patho-genic variants). There are few reports on clinico-pathological characteristics; one report compared 30 LFS breast cancers with 79 sporadic cases and showed a significantly higher rate of HER2 posi-tivity in the LFS group (67% vs. 25%, respectively; p<0.001)14). In addition, 65% of LFS breast cancers were bilateral. Our case had similar pathological characteristics and clinical course.408Figure 2　Pathological features of the surgical specimens