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Women who are heterozygous for deleterious BRCA1 germline mutations harbor a high risk of hereditary breast cancer. Previous Brca1‐heterozygous animal models do not recapitulate the breast cancer phenotype, and thus all currently used knockout models adopt conditional, mammary‐specific homozygous Brca1 loss or addition of Trp53 deficiency. Herein, we report the creation and characterization of a novel Brca1 mutant rat model harboring the germline L63X mutation, which mimics a founder mutation in Japan, through CRISPR‐Cas9–based genome editing. Homozygotes (Brca1L63X/L63X) were embryonic lethal, whereas heterozygotes (Brca1L63X/+) showed apparently normal development. Without carcinogen exposure, heterozygotes developed mammary carcinoma at a comparable incidence rate with their wild‐type (WT) littermates during their lifetime. Intraperitoneal injection of 1‐methyl‐1‐nitrosourea (25 or 50 mg/kg) at 7 weeks of age induced mammary carcinogenesis at comparable levels among the heterozygotes and their littermates. After exposure to ionizing radiation (0.1–2 Gy) at 7 weeks of age, the heterozygotes, but not WT littermates, displayed dose‐dependent mammary carcinogenesis with 0.8 Gy−1 excess in hazard ratio during their middle age; the relative susceptibility of the heterozygotes was more prominent when rats were irradiated at 3 weeks of age. The heterozygotes had tumors with a lower estrogen receptor α immunopositivity and no evidence of somatic mutations of the WT allele. The Brca1L63X/+ rats thus offer the first single‐mutation, heterozygous model of BRCA1‐associated breast cancer, especially with exposure to a DNA break‐inducing carcinogen. This implies that such carcinogens are causative and a key to breast cancer prevention in individuals who carry high‐risk BRCA1 mutations. [ABSTRACT FROM AUTHOR]

Disease sites of female genital tract cancers of BRCA1/2-associated hereditary breast and ovarian cancer (HBOC) are less understood than non-hereditary cancers. We aimed to elucidate the disease site distribution of genital cancers in women with the germline BRCA1 and BRCA2 pathogenic variants (BRCA1+ and BRCA2+) of HBOC. For the primary disease site, the proportion of fallopian tube and peritoneal cancer was significantly higher in BRCA2+ (40.5%) compared with BRCA1+ (15.4%) and BRCA− (no pathogenic variant, 12.8%). For the metastatic site, the proportion of peritoneal dissemination was significantly higher in BRCA1+ (71.9%) than BRCA− (55.1%) and not different from BRCA2+ (71.4%). With one of the most extensive patients, this study supported the previous reports showing that the pathogenic variants of BRCA1/2 were involved in the female genitalia's disease sites. [ABSTRACT FROM AUTHOR]

The frequency of microsatellite instability (MSI) is reportedly extremely low in breast cancer, despite widespread clinical expectations that many patients would be responsive to immune‐checkpoint inhibitors (ICI). Considering that some triple‐negative breast cancers (TNBC) responded well to ICI in a clinical trial and that a high density of tumor‐infiltrating lymphocytes (TILs) is frequently observed in other cancers with high levels of microsatellite instability (MSI‐H), we hypothesized that some TNBC with a high density of TILs would be MSI‐H. Medullary carcinoma (MedCa) of the breast, a rare histological type, is characterized by a high density of TILs. Considering that MedCa of the colon is often MSI‐H, we suspected that MedCa in breast cancer might also include MSI‐H tumors. Therefore, we conducted MSI tests on such breast cancers with a high density of TILs. The MSI status of 63 TIL‐high TNBC and 38 MedCa tumors, all from Asian women who had undergone curative surgery, were determined retrospectively. DNA mismatch repair (MMR) proteins and PD‐L1 expression were also investigated immunohistochemically. All samples were microsatellite stable, being negative for all microsatellite markers. TIL‐high TNBC with low MLH1 protein had higher levels of PD‐L1 in stromal immune cells (P =.041). MedCa tumors showed significantly higher PD‐L1 expression in immune cells than in TIL‐high TNBC (<.001). We found that MSI‐H tumors were absent in TIL‐high breast cancers. Examination of MMR proteins, not a purpose of Lynch syndrome screening, may merit further studies to yield predictive information for identifying patients who are likely to benefit from ICI. [ABSTRACT FROM AUTHOR]

Background: This study aimed to identify the clinical background and treatment outcomes of risk-reducing salpingo-oophorectomy (RRSO) in Japan for women with hereditary breast and ovarian cancer (HBOC). Methods: In the present retrospective observational study, we examined the Japanese HBOC Consortium's (JHC) database. This database contains 11,711 probands who received BRCA genetic testing, or their relatives, with any cancer in 2433 pedigrees. This study was supported by the registration committee of the JHC. Results: We analyzed 488 individuals diagnosed with HBOC, of which 153 (31.4%) underwent RRSO. Of the latter patients, 88 carried BRCA1 mutation (B1); 62 carried BRCA2 mutation (B2); and 3 carried both mutations. During a mean follow-up period of 2.6 years (range 0–12.6), one patient developed a primary peritoneal cancer (PPC). Clinical background comparison for individuals who underwent RRSO vs. those > 45 years of age who did not undergo RRSO revealed that significant factors were represented by B1 (p < 0.0001); child bearing (p < 0.00001); and breast cancer history (p < 0.01). However, family history of ovarian cancer and menopause status were not significantly different. Conclusion: Over 30% HBOC's in Japan underwent RRSO. In Japan, individuals with breast cancer history and B1 generally underwent RRSO, whereas those who did not bear a child mostly avoided RRSO. [ABSTRACT FROM AUTHOR]

About 60% of familial breast and ovarian cancers in Japan involve germline mutations of the BRCA1 or BRCA2 (BRCA½) genes. These genes contribute to genetic stability and DNA repair and act as tumor suppressor genes. Mutation analysis of the BRCA½ genes has improved our understanding of both common mutation patterns in Japanese patients and the clinicopathological features of BRCA½-related cancers. BRCA1-related breast cancers are characterized by poor prognosis, a low rate of estrogen receptor positivity, and histological predominance of solid-tubular carcinoma. BRCA1-related ovarian cancers are associated with a high frequency of serous adenocarcinoma and a good outcome. Further largescale studies are needed to delineate genotype-phenotype relations and penetrance in BRCA½-related breast and ovarian cancers in Japan. The development of systems for clinical genetics in Japan, including genetic counseling, has led to the increased use of genetic testing for the clinical management of BRCA½-related cancers. Three options are available for carriers of BRCA½ mutations: intensive surveillance, chemoprevention, and prophylactic surgery. Studies done in other countries indicate that prophylactic surgery effectively prevents the development of breast and ovarian cancers in carriers of BRCA½ mutations. However, prophylactic mastectomy remains controversial in Japan, and now systematic intensive surveillance is generally performed for the prevention of breast cancer in women at high risk. Early detection of ovarian cancer remains challenging, resulting in increased acceptance of the need for prophylactic oophorectomy in women at risk. This review summarizes experimental and clinical findings about familial breast and ovarian cancers, including data on Japanese patients. [ABSTRACT FROM AUTHOR]