The incidence of male breast cancer is less than 1% of the incidence of female breast cancer, making it a rare cancer. In addition to epidemiologic factors, such as aging, obesity, and radiation exposure, genetic factors are also involved in male breast cancer. Among these genetic factors are the two major causative genes, BRCA1 and BRCA2; however, ATM, CDH1, and PALB2 may also underlie the development of breast cancer in male patients. Genetic analyses of male breast cancers using multiple gene panel sequencing have rarely been conducted in Japan. Here, we performed multiple genetic tests in seven male patients with breast cancer patients. Using peripheral blood cells of the patients, immortalized B cells were established for genetic analysis. DNA was isolated from the immortalized B cells for panel sequencing analysis, including BRCA1/2 genes. Of the 7 patients, pathogenic variants (BRCA2 and TP53) were detected in two. Specifically, in the patient with the TP53 variant, a mosaic mutation was suspected from the variant allele frequencies. Unexpectedly, this variant was not detected by single-site genetic testing using the patient’s peripheral blood cells, saliva, or hair, suggesting that it was generated or amplified during the culture of immortalized B cells. Considering the findings, genetic counseling was provided for each patient. The genetic background of male patients with breast cancer must be analyzed to provide correct genetic counseling.

　Recently, microsatellite instability (MSI) tests have been widely used to identify MSI-high (MSI-H) among patients with various types of tumors. However, the incidence of these MSI-H cases, their prognosis, and rate at which patients are connected to genetic counseling have not yet been clarified. We report our experience with the treatment of MSI-H cases in our hospital. In this study, we investigated the results of MSI tests performed in clinical practice. A total of 203 patients were examined using MSI tests between April 2019 and December 2022. In all cancer cases (digestive, n=159; urinary, n=28; gynecological, n=12), the overall frequency of MSI-H was 5.4% (n=11). The original organs of the MSI-H tumors included the right-sided colon in five cases, the distal side of the stomach in five cases, and the prostate in one case. Only one patient with colon cancer received genomic counseling and was diagnosed with Lynch syndrome (with MLH-1 germline mutation). Immune checkpoint inhibitors (pembrolizumab) were used in 9 of the 11 MSI-H cases. There were no common clinical or histological characteristics in the MSI-H cases. Further studies are required.

　Hereditary breast and ovarian cancer (HBOC) is an autosomal dominant form of cancer susceptibility syndrome, which is caused by germline pathological variants of BRCA1 or BRCA2 in the narrow sense of the term. The selection of patients for BRCA examination to confirm HBOC is based on the HBOC practice guidelines of the Japanese Organization for Comprehensive Treatment of Hereditary Breast and Ovarian Cancer and the testing criteria of the NCCN guidelines, which differ in some respects, and therefore, so do the test subjects. The criteria for testing are partially different between the two guidelines, so the target population for testing is also different. In this study, we examined the degree to which both testing criteria were met in 58 of 220 patients who were tested positive for BRCA between January 2019 and November 2022 at our hospital. The number of BRCA1/2-positive patients who did not meet the HBOC and NCCN guidelines did not differ significantly, but there were some patients who did not meet the criteria due to cancer or family history of cancer. We believe that the testing criteria should be reviewed in order to increase the number of BRCA-positive patients in the future.

　Recently, insurance coverage for BRCA genetic testing has expanded, and the number of cases tested has increased. The result for INCONCLUSIVE is a rare case. This means that it was impossible to make a decision due to technical problems. Three cases were reported as INCONCLUSIVE, of the 399 cases of BRCA genetic testing in our hospital.

　Case 1 is a 34 years-old woman. No family history of breast or ovarian cancer. She was diagnosed with right breast cancer, cT1cN0M0 cStage I. She underwent preoperative BRCA genetic testing, and the result was INCONCLUSIVE for BRCA1 exon 21 to 24. An additional report diagnosed with NEGATIVE was received about one month after the initial report. Case 2 is a 53 years-old woman who had right breast cancer at 34 years-old. She underwent surgery for local recurrence. Her mother had breast cancer in her 60s. Case 3 is a 74 years-old woman. Her mother had breast cancer in her 70s. She was diagnosed as right breast cancer, cT1bN0M0 cStage I, and underwent surgery. Their BRCA genetic test results were INCONCLUSIVE for BRCA1 exon13, but no additional report was received.

　Even if the result is INCONCLUSIVE, we should consider about the risk of HBOC and respond carefully in each case.

　Li-Fraumeni syndrome (LFS) is a highly penetrant cancer syndrome associated with a germline pathogenic variant of TP53, which is responsible to develop premenopausal breast cancers. According to the NCCN guideline version 2 2024 for female LFS carriers, it is recommended to take annual breast MRI and mammography. It is also considered an option to undergo bilateral risk-reducing mastectomy with genetic counseling. LFS has been mostly diagnosed by single-gene testing among patients; who were estimated high risk according to the classic criteria of LFS or Chompret criteria. However, since multi-gene panel testing has recently become more common in some countries such as the United States, it has been revealed that there are some cases of LFS with different clinical features from conventional LFS. We present a case of LFS whose relative was diagnosed with LFS by a multi-gene panel test, and who had bilateral breast cancer which were diagnosed in the first breast surveillance. We have experienced 5 cases of LFS with breast cancer in our hospital. In order to clarify the clinicopathological characteristics of breast cancer in LFS, we examined the concordance between clinicopathological factors and diagnostic criteria in the five cases.

　An 83-year-old man underwent comprehensive genomic profiling (Guardant360^® CDx) during treatment for liver metastasis after surgery for rectal leiomyosarcoma. The results showed four kinds of TP53 pathogenic variants with different allele frequencies (P152L 53.12%, Y220C 0.9%, G266E 0.39%, F270L 0.16%). As the patient had a medical history of six malignant tumors, including gastric cancer at age 56 and colorectal cancer, TP53 P152L, with an allele frequency of 50% or more, was disclosed as a presumed germline pathogenic variant. After genetic counseling, a single-site test detected a pathogenic germline variant, and the patient was diagnosed with Li-Fraumeni syndrome. This case was really difficult to detect Li-Fraumeni syndrome using the clinical diagnostic criteria, and was diagnosed as having it after undergoing comprehensive genomic profiling. Therefore, we recognize the necessity for confirmatory testing even in elderly people.