Abstract P2-10-12: Relationship between predicted risks of carrying breast cancer susceptibility genes and the presence of germline variants in Japanese patients with primary breast cancer

Background: Breast cancer risk models are used to predict the risk of carrying a variant, for one of the most common breast cancer susceptibility genes such as BRCA1 and BRCA2, and the lifetime risk of developing breast cancer. The prediction of harboring a germline variant of the BRCA gene and the development of breast or ovarian cancer over time affects the decision-making for undergoing genetic testing and screening using imaging techniques as the common practice. For instance, the American Cancer Society and the National Comprehensive Cancer Network (NCCN) recommends screening using MRI in women with 20% or greater lifetime risk of having breast cancer. We aimed to investigate the prediction of these risks in Japanese women, particularly on the relationship between the presence of pathogenic germline variants and breast cancer susceptibility genes, using a cohort of 1016 primary breast cancer patients. Patients and Methods: We analyzed a cohort of Japanese patients with primary breast cancer who were treated at the Kyoto University Hospital and the related institutions or hospitals from the period of 2011 to 2016. The germline variants were examined for a set of 13 breast cancer susceptibility genes, using targeted-capture sequencing of pooled DNA, and it was found that 66 out of 1016 patients had pathogenic variants. These included 11 functionally well-established genes (BRCA1, BRCA2, TP53, PTEN, CDH1, STK11, NF1, PALB2, ATM, CHEK2, and NBN) and two additional genes (BARD1 and BRIP1), which are recommended for the screening of high-risk patients with hereditary breast cancer in the NCCN guidelines. Using this cohort, we studied the association of the calculated risk of carrying a germline variant of BRCA1/ BRCA2, using the Tyrer-Cuzick model Breast Cancer Risk Evaluation Tool, within the laboratory germline test results. Results: Pathogenic germline variants of BRCA1/ BRCA2 were carried by 54 (5.3%) out of the 1016 patients (12 cases of BRCA1 and 42 cases of BRCA2). According to the NCCN guidelines, which focus on Genetic/ Familial High-Risk Assessment: Breast and Ovarian, it was found that 500 out of 1016 (49.2%)patients were categorized for considering germline testing. In fact, 38 (7.6%) of the 500 patients, harbored a pathogenic germline variant of BRCA1/ BRCA2. In the remaining 516 patients, 16 (3.1%) harbored the pathogenic germline variant of BRCA1/ BRCA2. The predictive risks of the Tyrer-Cuzick model Breast Cancer Risk Evaluation Tool were recorded as follows: Area under the ROC curve, BRCA1 (area 0.750, 95% CI- 0.581-0.919), BRCA2 (area 0.741, 95% CI- 0.661-0.820), BRCA1 or BRCA2 (Area 0.749, 95% CI: 0.675-0.822), suggesting that the Tyrer-Cuzick model may be useful for the Japanese population. In the mammography breast density analysis, 484 patients showed almost entirely fat or scattered fibroglandular breast tissue, and 362 cases had heterogeneous or extreme fibroglandular breast tissue. In this study, the correlations of breast tissue density with age and breast or ovarian cancer familial history have been reported in greater detail. Discussion and Conclusions: In a retrospective cohort of 1016 Japanese patients with primary breast cancer, 5.3% had pathogenic germline variants of BRCA1/ BRCA2. In a group recommended by NCCN guidelines for considering genetic testing, the BRCA1/ BRCA2 variant rate was 7.6%. Predictive risks calculated by the Tyrer-Cuzick model similar with the known data. Further data are reported. Citation Format: Noriko Senda, Nobuko Kawaguchi-Sakita, Masahiro Kawashima, Yukiko Inagaki-Kawata, Kenichi Yoshida, Tomomi Nishimura, Masahiro Takada, Eiji Suzuki, Yuki Kataoka, Fumiaki Sato, Yoshiaki Matsumoto, Masae Torii, Hiroshi Yoshibayashi, Kazuhiro Yamagami, Shigeru Tsuyuki, Akira Yamauchi, Nobuhiko Shinkura, Hironori Kato, Yoshio Moriguchi, Ryuji Okamura, Norimichi Kan, Hirofumi Suwa, Shingo Sakata, Susumu Mashima, Fumiaki Yotsumoto, Tsuyoshi Tachibana, Mitsuru Tanaka, Takashi Inamoto, Masahiro Sugimoto, Seishi Ogawa, Masakazu Toi. Relationship between predicted risks of carrying breast cancer susceptibility genes and the presence of germline variants in Japanese patients with primary breast cancer [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P2-10-12.