Abstract P5-03-05: Comprehensive analysis of the prevalence of germline mutations and their association with somatic mutations in Chinese unselected breast cancer patients
Authors: Liao Ning , Chen Bo , Zhang Guochun , Ren Chongyang , Wang Yulei , Guo Liping , Cao Li , Wen Lingzhu , Li Kai , Jia Minghan , Li Cheukfai , Mok Hsiaopei , Wei Guangnan , Lin Jiali , Zhang Zhou , Hou Ting , Lizaso Analyn , Liu Jing 
Published: March 2020

Abstract
Background: The data on the prevalence of cancer-related germline mutations and the phenotypes associated with some rare mutations in Chinese breast cancer patients are limited. In this study, the mutation profile of a large cohort of unselected Chinese breast cancer patients were elucidated to determine the prevalence of likely pathogenic or pathogenic (LP/P) germline mutations and their association with clinicopathologic features as well as somatic mutations.Methods: To elucidate the genomic and somatic mutation profile of 524 Chinese breast cancer patients with various stages unselected for predisposing factors, targeted sequencing was performed using a panel consisting of 520 cancer-related genes including 62 cancer susceptibility genes for germline profile. To analyze the somatic mutation profile of the germline mutation carriers, the patients were divided into three groups according to germline mutations: BRCA1/2 (Germline-BRCA1/2), non-BRCA1/2 (Germline-others) and germline wild-type (gWT) groups.Results: A total of 58 patients (11.1%) carried 76 LP/P germline variants in 15 cancer predisposition genes. Germline BRCA1/2 mutations were detected in 29 (5.53%) patients; with 11 (2.10%) BRCA1 carriers and 18 (3.44%) BRCA2 carriers. In addition, LP/P germline mutations were detected in other genes including MUTYH (n=4), PALB2 (n=4), ATM (n=3), BRIP1 (n=3), CDH1 (n=3), RAD51C (n=3), CHEK2 (n=2), FANCA (n=2), PMS2 (n=2), TP53 (n=2), FANCI (n=1), FANCL (n=1) and PTEN (n=1). At least one VUS was identified in 490 (93.5%) patients. Young age (P=0.011), premenopausal status (P=0.013), and breast/ovarian cancer family history (P=0.001) were correlated with germline mutations. Furthermore, patients with Germline-BRCA1/2 had significantly more missense mutations (P=0.02) and less copy number amplification (P=0.04) than patients carrying Germline-others. Meanwhile, mutation types were comparable between Germline-others and gWT patients (P&gt;0.05). Furthermore, the somatic mutation rates for AKT1, CCND1, FGFR1 and PIK3CA varied among the three groups. No mutations in AKT1 and CCND1 were detected in the Germline-BRCA1/2 group. FGFR1 mutations were detected in 24% of the Germline-others group, while the Germline-BRCA1/2 and gWT groups had 10% and 9%, respectively. Moreover, PIK3CA mutations was significantly fewer in the Germline-BRCA1/2 group than Germline-Others (P=0.02) and gWT patients (P=0.002).Conclusions: Our study is the largest germline mutation study in unselected breast cancer patients in Southern China interrogating all breast or ovarian cancer-related genes listed in the US genetic guidelines. The inclusion of the 15 most common cancer susceptibility genes in cancer predisposition screening is important in the Chinese population for selecting the subset of breast cancer patients to receive multigene panel testing. Furthermore, our study also revealed the distinct somatic mutations profiles in germline mutation carriers, which contributes for a better understanding of the tumor characteristics of patients with LP/P germline mutations.
Citation Format: Ning Liao, Bo Chen, Guochun Zhang, Chongyang Ren, Yulei Wang, Liping Guo, Li Cao, Lingzhu Wen, Kai Li, Minghan Jia, Cheukfai Li, Hsiaopei Mok, Guangnan Wei, Jiali Lin, Zhou Zhang, Ting Hou, Analyn Lizaso, Jing Liu. Comprehensive analysis of the prevalence of germline mutations and their association with somatic mutations in Chinese unselected breast cancer patients [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 P5-03-05.