Background: HER2-low breast cancers were reported to have distinct clinicopathological characteristics from HER2-zero; however, the difference in their genetic features remains unclear. This study investigated the clinical and molecular features of breast tumors according to HER2 status. Methods: We analyzed the clinicopathological and genomic data of 523 Chinese women with breast cancer. Genomic data was generated by targeted next-generation sequencing (NGS) of breast tumor samples using a commercial 520 gene panel. The cohort was stratified according to HER2 status as HER2-zero (n = 90), HER2-low (n = 231), and HER2-positive (n = 202) according to their immunohistochemistry and fluorescence in situ hybridization results. Results: HER2-low breast tumors were enriched with hormone receptor-positive tumors, and who had lower Ki67 expression levels. Genes were differentially mutated across HER2 subgroups. HER2-low tumors had significantly more mutations involved in PI3K-Akt signaling than HER2-positive (p < 0.001) and HER2-zero breast tumors (p < 0.01). HER2-zero tumors had more mutations in checkpoint factors (p < 0.01), Fanconi anemia (p < 0.05), and p53 signaling and cell cycle pathway (p < 0.05) compared to HER2-low breast tumors. Compared with HER2-zero tumors, HER2-low tumors had significantly lower pathological complete response rates after neoadjuvant therapy (15.9% vs. 37.5%, p = 0.042) and proportion of relapsed/progressed patients across follow-up time points (p = 0.031), but had comparable disease-free survival (p = 0.271). Conclusion: Our results demonstrate the distinct clinical and molecular features and clinical outcomes of HER2-low breast tumors.

The complexity of breast cancer at the clinical, morphological and genomic levels has been extensively studied in the western population. However, the mutational genomic profiles in Chinese breast cancer patients have not been explored in any detail. We performed targeted sequencing using a panel consisting of 33 breast cancer-related genes to investigate the genomic landscape of 304 consecutive treatment-naïve Chinese breast cancer patients at Guangdong Provincial People's Hospital (GDPH), and further compared the results to those in 453 of Caucasian breast cancer patients from The Cancer Genome Atlas (TCGA). The most frequently mutated gene was TP53 (45%), followed by PIK3CA (44%), GATA3 (18%), MAP3K1 (10%), whereas the copy-number amplifications were frequently observed in genes of ERBB2 (24%), MYC (23%), FGFR1 (13%) and CCND1 (10%). Among the 8 most frequently mutated or amplified genes, at least one driver was identifiable in 87.5% (n=267) of our GDPH cohort, revealing the significant contribution of these known driver genes in the development of Chinese breast cancer. Compared to TCGA data, the median age at diagnosis in our cohort was significantly younger (48 vs. 58 years; P<0.001), while the distribution of estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor-2 (HER2) statuses were similar. The largest difference occurred in HR+/HER2- subtype, where 8 of the 10 driver genes compared had statistically significant differences in their frequency, while there were differences in 2 of 10 driver genes among the TNBC and HR+/HER2+ group, but none in the HR-/HER2+ patients in our cohort compared to the TCGA data. Collectively, the most significant genomic difference was a significantly higher prevalence for TP53 and AKT1 in Chinese patients. Additionally, more than half of TP53-mutation HR+/HER2- Chinese patients (~60%) are likely to harbor more severe mutations in TP53, such as nonsense, indels, and splicing mutations. We elucidated the mutational landscape of cancer genes in Chinese breast cancer and further identified significant genomic differences between Asian and Caucasian patients. These results should improve our understanding of pathogenesis and/or metastatic behavior of breast cancer across races/ethnicities, including a better selection of targeted therapies.

The data on the phenotypes associated with some rare germline mutations in Chinese breast cancer patients are limited. The difference in somatic mutation profiles in breast cancer patients with germline BRCA and non-BRCA mutations remains unexplored. We interrogated the germline and somatic mutational profile of 524 Chinese breast cancer patients with various stages unselected for predisposing factors using a panel consisting of 520 cancer-related genes including 62 cancer susceptibility genes. We divided the patients into three groups according to germline mutations: Germline-BRCA1/2, Germline-others (non-BRCA) and Others (non-carriers). A total of 58 patients (11.1%) carried 76 likely pathogenic or pathogenic (LP/P) germline variants in 15 cancer predisposition genes. Germline BRCA1/2 mutations were detected from 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 variant of uncertain significance (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. Germline-BRCA1/2 group was detected with more missense (P=0.02) and less copy-number amplification (P=0.04) than Germline-others group. Meanwhile, Germline-others group and Others group are very similar (P>0.05). The mutation rates of AKT1, CCND1, FGFR1, and PIK3CA were different among the three groups. By investigating all breast and ovarian cancer-related genes listed in the US genetic guidelines, we identified 15 cancer susceptibility genes frequently mutated in the germline of our population and must be included in cancer predisposition screening. Our study contributed a better understanding of the tumor characteristics of patients with LP/P germline mutations.

Clinical trials testing Janus kinase-1 (JAK1) inhibitors in cancers are under way. Whether the JAK1 mRNA levels in breast tumors correlates with outcome has not been evaluated. JAK1 expression was analyzed via the Oncomine database and Tumor IMmune Estimation Resource site. Tumor tissues from 57 breast cancer patients were used for qRT-PCR and immune infiltration assessment. JAK1 expression was significantly lower in breast invasive carcinoma compared with adjacent normal tissues. Public databases (Kaplan-Meier plotter and PrognoScan) showed that low JAK1 expression was associated with poorer survival. Data from The Cancer Genome Atlas (TCGA) showed that high JAK1 expression was associated with increased survival in both TNM I-II and TNM III-IV patients. JAK1 was inversely correlated with tumor size status, lymph node status, and TNM of breast cancer patients. JAK1 levels were correlated with the T cell transcript-enriched LYM metagene signature and was significantly lower in the low tumor infiltrating lymphocytes (TILs) group. JAK1 expression levels had significant positive correlations with infiltrating levels of CD8+ T cells, CD4+ T cells, macrophages, neutrophils, and dendritic cells in breast cancer and not with other B cells. In conclusion, JAK1 mRNA levels were correlated with prognosis and immune infiltrating levels in breast cancer.

Background: Comprehensive analysis of PI3K-AKT-mTOR pathway gene alterations in breast cancer may be helpful for targeted therapy.

HER2-positive breast cancer is a biologically and clinically heterogeneous disease. Based on the expression of hormone receptors (HR), breast tumors can be further categorized into HR positive and HR negative. Here, we elucidated the comprehensive somatic mutation profile of HR+ and HR− HER2-positive breast tumors to understand their molecular heterogeneity. In this study, 64 HR+/HER2+ and 43 HR-/HER2+ stage I-III breast cancer patients were included. Capture-based targeted sequencing was performed using a panel consisting of 520 cancer-related genes, spanning 1.64 megabases of the human genome. A total of 1119 mutations were detected among the 107 HER2-positive patients. TP53, CDK12 and PIK3CA were the most frequently mutated, with mutation rates of 76, 61 and 49, respectively. HR+/HER2+ tumors had more gene amplification, splice site and frameshift mutations and a smaller number of missense, nonsense and insertion-deletion mutations than HR-/HER2+ tumors. In KEGG analysis, HR+/HER2+ tumors had more mutations in genes involved in homologous recombination (P = 0.004), TGF-beta (P = 0.007) and WNT (P = 0.002) signaling pathways than HR-/HER2+ tumors. Moreover, comparative analysis of our cohort with datasets from The Cancer Genome Atlas and Molecular Taxonomy of Breast Cancer International Consortium revealed the distinct somatic mutation profile of Chinese HER2-positive breast cancer patients. Our study revealed the heterogeneity of somatic mutations between HR+/HER2+ and HR-/HER2+ in Chinese breast cancer patients. The distinct mutation profile and related pathways are potentially relevant in the development of optimal treatment strategies for this subset of patients.