Abstract P4-07-03: Comprehensive genomic analysis of Chinese breast cancer and clinical application

Background: Next generation sequencing (NGS) and the according target-based precision therapy has shown promising efficacy in many tumors. Here we report the genomic characteristics of Chinese breast cancer to support the development of more precise treatment strategy. Methods: Formalin fixed, paraffin embedded (FFPE) tumor samples and matched peripheral blood samples of 220 Chinese cancer patients including 218 females and 2 males were collected for NGS-based 450-genes panel assay. Pathological subtypes included 104 HR+/HER2-, 30 HR-/HER2+, 44 HR+/HER2+ and 42 triple negative breast cancers (TNBC). Assessed genomic alterations included single base substitution, short and long insertions/deletion, copy number variation, gene fusion and rearrangement. MSK breast cancer data was obtained from cBioPortal for comparing the difference between Chinese and Western patients. Results: The top mutated genes were TP53 (88.1%), PIK3CA (26.2%) and PTEN (21.4%) in TNBC; ERBB2 (86.7%), TP53 (86.7%), CDK12 (80.0%) and PIK3CA (23.3%) in HR-/HER2+ patients; ERBB2 (75%), TP53 (61.4%), CDK12 (54.5%) and PIK3CA (45.5%) in HR+/HER2+ patients. In HR+/HER2- patients, the most frequently mutated genes was PIK3CA (49.0%), followed by TP53 (30.8%) and GATA3 (27.9%), whereas the frequency of PIK3CA and GATA3 mutation were lower (41.6% and 19%, respectively) in Western patients. Although Alpelisib was approved by FDA in PIK3CA mutated HR+/HER2- patients, we observed PIK3CA mutation frequency had no difference among four subtypes. In this cohort, patients with PIK3CA mutation were significantly elder than patient without PIK3CA mutation (50 vs 47 years old, p=0.006). The hotspot mutations of PIK3CA (E542X, E545X and H1047X) accounted for 79.8% of PIK3CA mutations (71/89). Gene fusion/rearrangement was observed in 26% patients, in which 4 patients had gene fusions. Gene variations in homologous recombination pathway were found in 27.7% of patients. Among the 11.4% of patients with BRCA1/2 mutations, 11 patients harbored germline mutations and 19 patients had somatic mutations. Rearrangement accounted for 35% in somatic BRCA1/2 mutations. In the patients with germline BRCA1/2 mutation, 6 were HR+/HER2- patients who have been approved to use Olaparib. Based on the usage of CDK4/6 inhibitor in HR+/HER2- patients, this 450-genes panel enabled us to find that 41.3% HR+/HER2- patients had genes variations are related to CDK4/6 inhibitor resistance (CCND1, 18.3%; FGFR1 17.3%; NF1, 7.7%; MDM2, 6.7%; ESR1, 6.7% and RB1, 1.9%). The median TMB was 4.3 Muts/Mb in the whole cohort and patients with KMT2C mutations had significantly higher TMB (5.5 vs 3.8 Muts/Mb, p=0.004). In addition, Chinese breast cancer patients had a significantly higher frequency of KMT2C mutations compared to western patients (11.4% vs 1.4%, p Citation Format: Ning Liao, Guochun Zhang, Bo Chen, Yulei Wang, Kai Li, Chongyang Ren, Hsiaopei Mok, Li Cao, Lingzhu Wen, Minghan Jia, Cheukfai Li, Liping Guo, Guangnan Wei, Jiali Lin, Jiangguo Lai, Honglin Guo, Wenjing Wang, Shiyue Zhang, Zhijian Song, Jian Wang, Hui Chen, Jinwei Hu, Weifeng Wang, Weiwei Shi, Kai Wang. Comprehensive genomic analysis of Chinese breast cancer and clinical application [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 P4-07-03.