Search

Background: Germline DNA damage repair (DDR) mutations has been associated with increased cancer risk, PARP inhibitor therapeutic opportunity for breast cancer (BC) patients. However, the profile of germline mutations in BC covering comprehensive DDR genes remains unclear. Methods: A total of 341 women with breast cancer who tested 102 germline related genes (including 50 DDR genes) between April 2021 to May 2022 in Guangdong Provincial People’s Hospital were identified. Variants were classified into pathogenic, likely pathogenic, variant of uncertain significance (VUS), likely benign and benign groups according to the ACMG/AMP Standards and Guidelines. We defined pathogenic and likely pathogenic variants as deleterious mutations. Results: The median age of 341 breast cancer patients was 48 (range, 20-89) at the first diagnosis of BC. A total of 47 patients (13.78%) carried 53 deleterious germline variants in 21 cancer predisposition genes, 16 of which were DDR genes. DDR deleterious mutations were detected in genes including BRCA2 (n=18), BRCA1(n=7), FANCA (n=4), PMS2 (n=4), PALB2(n=2), RECQL4(n=2), PALB2 (n=2), etc. The younger age at diagnosis (less than 40-year-old) were significantly associated with deleterious mutations in DDR pathway(P=0.02). At least one VUS was identified in 238 (69.79%) patients. The top 5 DDR VUS genes were FANCM (n=21), ATM (n=20), RAD54L (n=17), FANCD2 (n=15) and ATR (n=14). Breast or ovarian cancer family history were significantly correlated with VUS germline mutations in DDR pathway(P=0.039). Interesting, we found that patients with pCR efficacy of neoadjuvant therapy were more likely to have VUS mutations in DDR pathway (table 1). Conclusion: We provided a comprehensive view of germline DDR gene mutations in BC patients and also analyzed the association between clinical characteristics and germline DDR mutation status. DDR mutations are prevalent in Chinese BC patients. Patients with younger and breast or ovarian cancer family history were more likely to carry DDR alterations. Moreover, patients with higher frequency of DDR VUS mutations may benefit from neoadjuvant therapy. Table 1. Clinicopathological characteristics between germline mutation carriers and non-carriers Citation Format: Ning Liao, Li Cao, Guochun Zhang, Junyun Wang, Airong Yang, Yulei Wang, Kai Li, Lingzhu Wen, Chongyang Ren, Minghan Jia, Cheukfai Li, Hsiaopei Mok, Bo Chen, Jianguo Lai, Weikai Xiao. Comprehensive analysis of DNA damage repair gene germline mutations in Chinese breast cancer patients [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P5-12-06.

There were limitations existing in programmed cell-death ligand 1 (PD-L1) as predictive biomarkers for breast cancer (BC), hence exploring the correlation between PD-L1 levels and other biomarkers in BC may become a very useful therapeutic clinical tool.A total of 301 Chinese patients with different BC subtypes including 47 HR+/HER2+, 185 HR+/HER2-, 38 HR-/HER2+, and 31 triple-negative breast cancer (TNBC) were enrolled in our study. Next-generation sequencing based Yuansu450 gene panel was used for genomic alteration identification and PD-L1 expression was tested using immunohistochemistry.The most prevalent BC-related mutations were TP53 mutations, followed by mutations in PIK3CA, ERBB2, CDK12, and GATA3 in our Chinese cohort. We found that mutations DDR2 and MYCL were only mutated in HR-/HER2+ subtype, whereas H3-3A and NRAS mutations were only occurred in HR-/HER2- subtype. The percentage of patients with PD-L1-positive expression was higher in patients with HR-/HER2- mainly due to the percentage of PD-L1-high level. Mutational frequencies of TP53, MYC, FAT4, PBRM1, PREX2 were observed to have significant differences among patients with different BC subtypes based on PD-L1 levels. Moreover, a positive correlation was observed between TMB and PD-L1 level in HR+/HER2- subtype, and showed that the proportion of patients with high PD-L1 expression was higher than that of patients with low PD-L1 expression in the HR+/HER2- and HR+/HER2+ cohorts with high Ki67 expression.The genomic alterations based on PD-L1 and other biomarkers of different cohorts may provide more possibilities for the treatment of BC with different subtypes.

Lingzhu Wen,1,* Guochun Zhang,1,* Chongyang Ren,1,* Xuerui Li,1 Hsiaopei Mok,1 Minghan Jia,1 Yulei Wang,1 Bo Chen,1 Kai Li,1 Li Cao,1 Cheukfai Li,1 Weikai Xiao,1 Jianguo Lai,1 Jiali Lin,1 Guangnan Wei,1 Yingzi Li,1 Yuchen Zhang,1 Xiaoqing Chen,2 Ning Liao1 1Department of Breast Cancer, Guangdong Provincial People’s Hospital (Guangdong Academy of Medical Sciences), Guangzhou, Guangdong, People’s Republic of China; 2Department of Breast Surgical Oncology, Foshan Maternity and Children’s Healthcare Hospital Affiliated to Southern Medical University, Foshan, Guangdong, People’s Republic of China*These authors contributed equally to this workCorrespondence: Ning LiaoDepartment of Breast Cancer, Guangdong Provincial People’s Hospital (Guangdong Academy of Medical Sciences), No. 106, Zhongshan 2nd Road, Yuexiu District, Guangzhou, Guangdong, People’s Republic of ChinaTel/Fax +86 20-83827812Email syliaoning@scut.edu.cnPurpose: This study aimed to investigate AKT gene mutation status in Chinese breast cancer patients.Methods: The study included 411 breast cancer patients hospitalized in Guangdong Provincial People’s Hospital (GDPH) from June 1, 2017 to September 27, 2018. Mastectomy or breast conserving surgery was performed, and tissue samples were subjected to next-generation sequencing (NGS) to determine AKT gene mutation status. Meanwhile, the expression of human epidermal growth factor receptor 2 (Her2), progesterone receptor (PR), and estrogen receptor (ER) was analyzed by immunohistochemistry staining. The Cancer Genome Atlas (TCGA) database was used for comparative studies.Results: Patients in the GDPH cohort had an older age (P < 0.001), higher postmenopausal rate (P < 0.001), larger tumor size (P < 0.001), higher histologic type of infiltrating duct cancer (P < 0.001), higher metastatic rate (P < 0.001), higher expression of ER (P = 0.015) and HER2 (P < 0.001), and higher percentage of the HR/HER2 subtype (P < 0.001) than those in the TCGA cohort. The GDPH cohort displayed lower rates of overall AKT and AKT3 mutation (P < 0.001), but a higher AKT1 mutation rate (P < 0.0001) compared with the TCGA cohort. Notably, the NGS studies identified missense mutation and copy number amplification as the most common AKT variation type in the GDPH and TCGA cohorts, respectively. Specifically, E17K mutation in AKT1 was predominantly detected in GDPH cohort, while being absent in TCGA cohort. Moreover, in the GDPH cohort, AKT variation was correlated with a number of clinicopathological variables, including age over 50, HER2-, HR+/HER2-, and PR+.Conclusion: Patients in the GDPH cohort had lower rates of AKT and AKT3 mutation and higher AKT1 mutation rate than those in the TCGA cohort, while harboring missense mutations detected predominantly as E17K mutation in AKT1. In GDPH cohort, there were correlations between AKT mutation and the clinicopathological characteristics of patients.Keywords: AKT, next-generation sequencing, breast cancer, somatic mutations, population study

Background Immunotherapies such as PD-L1 inhibitors have shown promising efficiency in breast cancer (BC) patients. However, treatment responses for immunotherapies are diverse since the immunogenicity of breast cancer is heterogeneous. Specific subtypes such as hormone receptor (HR)-positive, human EGF receptor 2 (HER2)-positive, and triple-negative breast cancer (TNBC) have shown heterogeneity in immunogenicity. Therefore, precisely identification of patients potentially benefit from immunotherapy is important. Previous studies have proved PD-L1 expression and tumor mutational burden (TMB) as predictive biomarkers for immunotherapy. Here, we report the PD-L1 expression and TMB status in Chinese BC patients with different subtypes. Using comprehensive molecular analysis, we also characterized the genomic features related to these biomarkers. Methods Tumor samples from 112 Chinese patients with BC were collected and subjected to next-generation sequencing (NGS) and immunohistochemical (IHC) analysis. NGS were performed in a laboratory accredited by College of American Pathologists (CAP) and certified by Clinical Laboratory Improvement Amendments (CLIA) using validated panel targeting 450 cancer genes. Genomic alterations, included including single base substitution, short and long insertions/deletion (Indel), copy number variation, gene fusion, and rearrangement, were assessed. Tumor mutational burden (TMB) was measured by an algorithm developed in-house. Tumor tissues were analyzed for PD-L1 expression by IHC with 22C3 or 28-8 antibodies, respectively. Results The 112 Chinese BC patients consisted of 87 HR+ (77.7%), 19 TNBC (17.0%) and 6 HR-/ HER2 + (5.3%), with a median age of 47.5 years old (range 24-81). Of all patients, 42.0% were positive for PD-L1 expression (CPS≥1), including 30.4% PD-L1 (1≥CPS>10) and 11.6% PD-L1 (CPS≥10). PD-L1 expression were observed in HR+ BCs (41.4%) as well as in TNBC (47.4%) and HR-/ HER2+ (33.3%) subtypes, no significant difference were observed among the three subtypes. 8.9% patients were TMB-High (≥10 muts/Mb) with median TMB of 3.4 muts/Mb (range 0-80.8). TMB was slightly correlated with PD-L1 expression (Kendall tau = 0.241; P =0.01). 17.0% of PD-L1 positive patients and 3.1% of PD-L1 negative patients were TMB-High (p=0.016). Patients with PD-L1 CPS≥10 had significantly higher median TMB (7.1 vs. 3.1 muts/Mb, p Conclusion Our data shows that the PD-L1 expression has no significant difference among HR+, TNBC and HR-/ HER2+ subtypes. These data provide the hypothesis that PD-L1 expression positive in different subtype breast cancers may benefit from immune treatment, including HER2 and Luminal subtypes. Otherwise, there was a correlation between PD-L1 expression and TMB, High TMB was also observed in PD-L1 negative patients, which may enrich the subgroup of patients who could benefit from immunotherapy. The verification of integrated predictive biomarkers for immunotherapy in BC is further needed. Citation Format: Ning Liao, Cao Li, Jundong Wu, Bo Chen, Guochun Zhang, Xueri Li, Liping Guo, Guangnan Wei, Jiali Lin, Yingzi Li, Yuchen Zhang, Hsiaopei Mok, Chongyang Ren, Yulei Wang, Kai Li, Cheukfai Li, Lingzhu Wen, Minghan Jia, Tengjiao Lin, Chunyan Cheng. Pd-l1 expression among different subtypes of chinese breast cancer patients [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS17-44.

Purpose Somatic alteration of phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha (PIK3CA) is a crucial therapeutic target in breast cancer (BC) and PI3Kα-specific inhibitor Alpelisib has been used in clinics. This study investigates the PIK3CA alterations in Chinese and Caucasians BC patients for the purpose of selecting anti-PI3K therapy. Methods The molecular profile of the PIK3CA gene was analyzed in 412 Chinese patients with untreated invasive BC using a 540 gene next-generation sequencing panel. The results were compared with data of the Caucasian BC patients in The Cancer Genome Atlas (TCGA-white). Results PIK3CA alterations were frequently found in BC of estrogen receptor (ER) positive (49.3%, p = 0.024), low ki67 proliferation index (58.3%, p = 0.007) and low pathological grade (grade I/II/III 80%, 53.4%, 35.9%, p p p = 0.01). Across four molecular subtypes, ER + /human epidermal growth factor receptor 2 positive (HER2 +) tumors harbored the most PIK3CA alterations (51.6%), while ER-/HER2- harbored the least alteration (30.0%) but the most copy number amplification (19.05%). Conclusion PIK3CA alterations prevail in Chinese BC patients and have different molecular features compared to that of Caucasians. The results provide precise annotations of PIK3CA genomic alterations of Chinese in the context of application of PIK3CA inhibitor.

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.

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.

Purpose: Somatic alterations of PIK3CA gene is an important therapeutic target in breast cancer (BC). The PI3Kα-specific inhibitor alpelisib was remarkably active against PIK3CA-mutated, HR-positive/HER2-negative BC in the SOLAR-1 trial. We hypothesized that PIK3CA alterations in Chinese BC patients across different molecular subtypes might differ from other ethnic groups and this information would be useful for selecting anti-PI3K therapy. Methods: The molecular profile of the PIK3CA gene was analyzed in 412 Chinese untreated invasive BC patients with ER/HER2 molecular subtypes, using a 540 gene next-generation sequencing panel. The results were compared to the molecular profile of Caucasian breast cancer patients in The Cancer Genome Atlas(TCGA-white). Results: Compared to wild type, PIK3CA alterations were more frequent in the ER+ subtype (49.3%, p=0.024), and tumors with low ki67 proliferation (58.3%, p=0.007) and low histological grade (grade I/II/III 80%, 53.4%, 35.9%, p Citation Format: Minghan Jia, Ning Liao, Bo Chen, Guochun Zhang, Yulei Wang, Xiaoqing Chen, Liping Guo, Li Cao, Hsiaopei Mok, Chongyang Ren, Kai Li, Cheukfai Li, Lingzhu Wen, Jiali Lin, Guangnan Wei, Zhou Zhang, Charles M Balch. PIK3CA somatic alterations in 412 chinese invasive breast cancers: Higher frequency of mutant H1047R detected by next generation sequencing compared to breast cancer in caucasians [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 P4-09-11.

OBJECTIVE: N6-methyladenosine (m6A) is a common RNA modification on eukaryotic mRNA and some of the m6A regulatory proteins play a crucial role in breast cancer. However, the copy number variations for m6A regulatory proteins and their role in clinicopathological characteristics and survival in breast cancer remain unclear. METHODS: In this study, we screened the m6A related genes alterations in breast cancer by analyzing the Molecular Taxonomy of Breast Cancer International Consortium and The Cancer Genome Atlas database, and further analyzed the clinical prognostic value of YTHDF1 amplification. RESULTS: The YTH domain family (YTHDF3 and YTHDF1) amplification exhibited higher alteration rates among 10 m6A regulatory genes. YTHDF1 and YTHDF3 amplification resulted in higher mRNA expression (P< 0.0001). Protein expression of YTHDF1 and YTHDF3 were higher in breast cancer (P< 0.0001). YTHDF1 amplification presented a high correlation with worse clinicopathological characteristics and overall survival in patients with breast cancer. Cox regression analysis showed that YTHDF1 amplification was an independent risk factor for 10-year overall survival in breast cancer (Hazard ratio: 1.663; 95% confidence interval: 1.298–2.131; P< 0.001). Gene set enrichment analysis revealed that the downstream target of YTHDF1 may be related to MYC signaling regulation and T cell differentiation. Moreover, YTHDF1 amplification and high expression resulted in lower immune cell infiltration. YTHDF1 knockdown retrained proliferation, migration and invasion in breast cancer cells in vitro. CONCLUSIONS: We found significant worse clinical characteristics and lower immune infiltrates in patients with YTHDF1 amplification. The findings indicate that YTHDF1 amplification may be a potential target for the treatment of breast cancer.

Little is known about the host-tumor interaction in the lymph-node basin at a single cell level. This study examines single cell sequences in breast cancer nodal metastases of a patient with triple-negative breast cancer.The primary breast tumor, sentinel lymph node, an adjacent lymph node with metastatic involvement and a clinically normal-appearing lymph node were collected during surgery. Single-cell sequencing was performed on all four specimens.14,016 cells were clustered into 6 cell subpopulations. Cancer cells demonstrated the molecular characteristics of TNBC basal B subtype and highly expressed genes in the MAPK signaling cascade. Tumor-associated macrophages regulated antigen processing and presentation and other immune-related pathways to promote tumor invasion. CD8 + and CD4 + T lymphocytes concentrated more in sentinel lymph node and mainly stratified into two transcriptional states. The immune-cell amount variation among primary tumor, sentinel and normal lymph nodes showed a similar tendency between the sc-RNA-seq profile of TNBC samples and a previous reported bulk RNA-seq profile of a breast cancer cohort, including all four breast cancer subtype samples.Single-cell sequencing analysis suggested that the sentinel lymph node was the initial meeting site of tumor infiltration and immune response, where partial T lymphocytes perform anti-tumor activity, while other T cells exhibit an exhausted state. We proposed a molecular explanation to the well-established clinical principle that the 5-year and 10-year survival outcomes were noninferior between SLND and ALND.

BackgroundTriple-negative breast cancer (TNBC) is refractory and heterogeneous, comprising various entities with divergent phenotype, biology, and clinical presentation. As an aggressive subtype, Chinese TNBC patients with special morphologic patterns (STs) were restricted to its incidence of 10-15% in total TNBC population.MethodsWe recruited 89 patients with TNBC at Guangdong Provincial People’s Hospital (GDPH) from October 2014 to May 2021, comprising 72 cases of invasive ductal carcinoma of no-special type (NSTs) and 17 cases of STs. The clinical data of these patients was collected and statistically analyzed. Formalin-fixed, paraffin-embedded (FFPE) tumor tissues and matched blood samples were collected for targeted next-generation sequencing (NGS) with cancer-related, 520- or 33-gene assay. Immunohistochemical analysis of FFPE tissue sections was performed using anti-programmed cell death-ligand 1(PD-L1) and anti-androgen receptor antibodies.ResultsCases with NSTs presented with higher histologic grade and Ki-67 index rate than ST patients (NSTs to STs: grade I/II/III 1.4%, 16.7%,81.9% vs 0%, 29.4%, 58.8%; pTP53 (88.7%), PIK3CA (26.8%), MYC (18.3%) in NSTs, and TP53 (68.8%), PIK3CA (50%), JAK3 (18.8%), KMT2C (18.8%) in STs respectively. Compared with NSTs, PIK3CA and TP53 mutation frequency showed difference in STs (47.1% vs 19.4%, p=0.039; 64.7% vs 87.5%, p=0.035).ConclusionsIn TNBC patients with STs, decrease in histologic grade and ki-67 index, as well as increase in PD-L1 and AR expression were observed when compared to those with NSTs, suggesting that TNBC patients with STs may better benefit from immune checkpoint inhibitors and/or AR inhibitors. Additionally, lower TP53 and higher PIK3CA mutation rates were also found in STs patients, providing genetic evidence for deciphering at least partly potential mechanism of action.

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.

BackgroundThe relationship between body mass index (BMI) and the prognosis or treatment response in patients with breast cancer has been demonstrated in previous studies, but the somatic mutation profiles in breast cancer patients with different BMIs have not been explored.MethodsIn the present study, the somatic mutation profiles in 421 female breast cancer patients who were stratified into three subgroups based on BMI (normal weight, overweight/obese, and underweight) were investigated. Capture-based targeted sequencing was performed using a panel comprising 520 cancer-related genes.ResultsA total of 3547 mutations were detected in 390 genes. In breast cancer patients with different BMI statuses, the tumors exhibited high mutation frequency and burden. TP53 was the most common gene in the three groups, followed by PIK3CA, ERBB2, and CDK12. Meanwhile, the mutation hotspots in TP53 and PIK3CA were the same in the three BMI groups. More JAK1 mutations were identified in underweight patients than those in normal patients. Except for JAK1, differentially mutated genes in postmenopausal patients were completely different from those in premenopausal patients. The distribution of mutation types was significantly different among BMI groups in the postmenopausal group. Underweight patients in the postmenopausal group harbored more TP53 mutations, more amplifications, and more mutations in genes involved in the WNT signaling pathway.ConclusionsOur next-generation sequencing (NGS)-based gene panel analysis revealed the gene expression profiles of breast cancer patients with different BMI statuses. Although genes with high mutation frequency and burden were found in different BMI groups, some subtle differences could not be ignored. JAK1 mutations might play a vital role in the progression of breast cancer in underweight patients, and this needs further analysis. Postmenopausal underweight patients with breast cancer have more aggressive characteristics, such as TP53 mutations, more amplifications, and more mutations in genes involved in the WNT signaling pathway. This study provides new evidence for understanding the characteristics of breast cancer patients with different BMIs.

e15120 Background: Trop2 has been confirmed to enhance tumor proliferation, metastasis and invasion in various epithelial tumors. Breast cancer (BC) patients with high Trop2 protein expression have better prognosis and objective response rates. Thus, this study aimed to explore potential biomarker associated with Trop2 protein expression in BC. Methods: BC patients with complete clinical parameters were enrolled, including age, estrogen receptor (ER) status, progesterone receptor (PR) status, human epithelial growth factor receptor 2 (HER2 status), molecular subtype, Ki67 status, T stage, N stage, TNM stage, PD-L1 and Trop2 protein expression level. Univariate and multivariate ordinal logistic regression analyses were performed to identify the independent factor for Trop2 protein expression level. Immunohistochemical analysis was conducted to detect the protein expression level of Trop2 in BC. Kaplan–Meier analysis and the log-rank test were executed to assess the survival difference between low- and high- gene expression level of Trop2. Results: A total of 65 BC patients from the Guangdong Provincial People’s Hospital were included. Based on the univariate and multivariate ordinal logistic regression analyses, Ki67 status was the only independent factor for Trop2 protein expression level (P < 0.05). This finding revealed that BC patients with higher Ki67 status may harbor higher Trop2 protein expression level. According to cBioPortal database, the mutation rate of Trop2 was 2.1% and mutation type was amplification. BC patients with low Trop2 gene expression level had significantly greater survival prognosis (P < 0.05). Conclusions: We performed the comprehensive analysis of the Trop2 in BC patients. It has the potential to guide individualized targeted treatment in BC patients.

e12570 Background: Little is known about the host-tumor interaction in the lymph node basin at a single cell level. This study examines single cell sequences in breast cancer nodal metastasis of a patient with triple negative breast cancer. Methods: The primary breast tumor, sentinel lymph node, an adjacent lymph node with metastatic involvement and a clinically normal-appearing lymph node were collected during operation. Single-cell sequencing was performed on all specimens. Results: 14,016 cells were clustered as 6 cell populations. Cancer cells demonstrated the molecular characteristics of TNBC basal B subtype and highly expressed genes in the MAPK signaling cascade. Tumor associated macrophages regulated antigen processing and presentation and other immune-related pathways to promote tumor invasion. CD8+ and CD4+ T lymphocytes concentrated more in sentinel lymph node and mainly stratified as two transcriptional states. Conclusions: The first single cell report investigates the host-tumor interaction in the lymph node basin of triple-negative breast cancer. Single-cell sequencing analysis suggested that the sentinel lymph node was the initial meeting site of tumor infiltration and immune response, where partial T lymphocytes perform anti-tumor activity while other T cells exhibit an exhaustion state. We proposed a molecular explanation to the well-established clinical principle that the 5-year and 10-year survival outcomes were noninferior between sentinel lymph node dissection (SLND) and axillary lymph node dissection (ALND).

Purpose Despite the therapeutic success of existing HER2-targeted therapies, tumors respond quite differently to them. This study aimed at figuring out genetic mutation profile of Chinese HER2-positive patients and investigating predictive factors of neoadjuvant anti-HER2 responses. Methods We employed two cohorts. The first cohort was comprised of 181 HER2-positive patients treated at Guangdong Provincial People’s Hospital from 2012 to 2018. The second cohort included 40 patients from the first cohort who underwent HER2-targeted neoadjuvant chemotherapy. Genetic mutations were characterized using next-generation sequencing. We employed the most commonly used definition of pathological complete response (pCR)-eradication of tumor from both breast and lymph nodes (ypT0/is ypN0). Results In Chinese HER2-positive breast cancer patients, TP53 (74.6%), CDK12 (64.6%) and PIK3CA (46.4%) have the highest mutation frequencies. In cohort 2, significant differences were found between pCR and non-pCR groups in terms of the initial Ki67 status, TP53 missense mutations, TP53 LOF mutations, PIK3CA mutations and ROS1 mutations (p = 0.028, 0.019, 0.005, 0.013, 0.049, respectively). Furthermore, TP53 LOF mutations and initial Ki67 status (OR 7.086, 95% CI 1.366–36.749, p = 0.020 and OR 6.007, 95% CI 1.120–32.210, p = 0.036, respectively) were found to be predictive of pCR status. Conclusion TP53 LOF mutations and initial Ki67 status in HER2-positive breast cancer are predictive of pCR status after HER2-targeted NACT.

B cells play a crucial role in alloreactivity of organ transplant rejection and graft versus host diseases (GVHD). Over the past decade, it has been well recognized that B-cell infiltration in allografts and de novo donor-specific antibodies (DSA) were strongly associated with severe graft rejection and loss, as well as glucocorticoid resistance. Emerging evidence has demonstrated that Follicular T helper (Tfh) cells are key effectors to promote the proliferation and differentiation of B cells into antibody-producing plasmablasts and memory B cells. T-follicular regulatory (Tfr) cells are a recently recognized cell population that has a negative regulatory role on Tfh cells in the follicle, preventing incessant antibody production. It is still less clear how those humoral immunoreactive cells affect transplant rejection and allograft loss. This review focuses on the production and function of Tfr/Tfh cells in the transplant environment. Better understanding of the functions and mechanisms of Tfr/Tfh cells will help to design new strategies to prevent allograft rejection and prolong graft survival.

BACKGROUND Poor transplant outcome was observed in donation after brain death followed by circulatory death (DBCD), since the donor organs suffered both cytokine storm of brain death and warm ischemia injury. MicroRNAs (miRNAs) have emerged as promising disease biomarkers, so we sought to establish a miRNA signature of porcine DBCD and verify the findings in human liver transplantation. MATERIAL AND METHODS MiRNA expression was determined with miRNA sequencing in 3 types of the porcine model of organ donation, including donation after brain death (DBD) group, donation after circulatory death (DCD) group, and DBCD group. Bioinformatics analysis was performed to reveal the potential regulatory behavior of target miRNA. Human liver graft biopsy samples after reperfusion detected by fluorescence in situ hybridization were used to verify the expression of target miRNA. RESULTS We compared miRNA expression profiles of the 3 donation types. The porcine liver graft miR-146b was significantly increased and selected in the DBCD group versus in the DBD and DCD groups. The donor liver expression of human miR-146b-5p, which is homologous to porcine miR-146b, was further examined in 42 cases of human liver transplantations. High expression of miR-146b-5p successfully predicted the post-transplant early allograft dysfunction (EAD) with the area under the ROC curve (AUC) 0.759 (P=0.004). CONCLUSIONS Our results revealed the miRNA signature of DBCD liver grafts for the first time. The miR-146b-5p may have important clinical implications for monitoring liver graft function and predicating transplant outcomes.

Background: Numerous researches have demonstrated that miR-142-5p plays significant roles in several cancers, although the functional characteristic of miR-142-5p in breast cancer has not been determined. This study is designed to explore the biological significance of miR-142-5p in breast cancer clinical implication and mechanism of action. Methods: The differential expression patterns of miR-142-5p and Sorbin and SH3 domain-containing protein 1 and correlations between them and clinical significances were analyzed based on data from database. The expression levels of miR-142-5p in breast cancer cells were detected using quantitative real-time polymerase chain reaction. Cell counting kit-8, transwell, and wound healing assays were used to explore the potential functions of miR-142-5p in breast cancer cells. In addition, bioinformatics prediction analysis and luciferase reporter assay were utilized to predict and identify the potential target gene of miR-142-5p. A rescue experiment was conducted by transfecting miR-142-5p inhibitors and si-Sorbin and SH3 domain-containing protein 1 into cells to explore miR-142-5p/Sorbin and SH3 domain-containing protein 1 pairs on breast cancer cells behaviors. Results: The analysis results showed that miR-142-5p was highly expressed in patients with breast cancer, while Sorbin and SH3 domain-containing protein 1 presented a trend of low expression. The clinical significances analysis suggested that the overexpression of miR-142-5p is closely correlated with metastasis, while low expression of Sorbin and SH3 domain-containing protein 1 is correlated with clinicopathological characteristics and poor overall survival in patients with breast cancer. In vitro exploration, the expression of miR-142-5p was upregulated in breast cancer cells and inhibition of miR-142-5p expression significantly reduced the proliferation, invasion, and migration of breast cancer cells. Through rescue experiments, breast cancer cells proliferation, invasion, and migration reduction induced by silencing of miR-142-5p were reversed via knockdown Sorbin and SH3 domain-containing protein 1. Conclusion: Our findings insinuate that miR-142-5p functions as a positive regulator of promoting breast cancer cells biological behaviors and clinical metastasis, possibly regulated by targeting Sorbin and SH3 domain-containing protein 1, thus providing valuable information in the development of preventive or even therapeutic strategies for utilizing miR-142-5p as a promising target.

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.

BACKGROUND: 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. METHODS: 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). RESULTS: 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

N6-methyladenosine (m6A) is a common RNA modification on eukaryotic mRNA and several m6a regulatory proteins, which plays a crucial part in breast cancer. But the copy number variations (CNVs) for m6a regulatory proteins and their role in pathogenesis and progression in breast cancer is still unclear. By analyzing the Molecular Taxonomy of Breast Cancer International Consortium (METABRIC) and the cancer genome atlas (TCGA database), we screened CNVs of ten m6A regulatory genes, including YTHDF3, YTHDF1, FTO, YTHDC1, ALKBH5, METTL3, WTAP, METTL14, YTHDF2, YTHDC2. Among them, YTHDF3 and YTHDF1 amplification had higher alteration rates among ten m6A regulatory genes. YTHDF1 and YTHDF3 amplification resulted in higher mRNA expression (P Univariate and multivariate Cox proportional hazard analysis for 10-year overall survivalUnivariateUnivariateHR95% CIP valueHR95% CIP valueNode status1.7181.566-1.885 Citation Format: Cheukfai Li, Guochun Zhang, Yulei Wang, Bo Chen, Kai Li, Li Cao, Chongyang Ren, Lingzhu Wen, Minghan Jia, Hsiaopei Mok, Jianguo Lai, Weikai Xiao, Xuerui Li, Ning Liao. YTHDF1 amplification associates with clinicopathological featuresand predicts worse survival in breast cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5912.

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>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.

Summary Background Paediatric liver allografts sometimes are allocated to adult recipients when there are no suitable paediatric recipients on the waiting list. However, debate exits regarding the reported outcomes of liver transplants using such small grafts. Methods Records from adult patients undergoing liver transplantation between February 2010 and January 2016 who received whole grafts from paediatric (≤ 13 years) donors or ideal deceased adult (18–35 years) donors were reviewed. Patient and graft survival, post-transplant liver function, and complications between the two groups were compared. Results The baseline characteristics were comparable, except that the paediatric donor allografts had smaller size. The 3-month, 1-year, and 3-year rates of patient survival were 91.3%, 85.2%, and 85.2% in the paediatric donor group and 93.4%, 88.9%, and 85.0% in the adult donor group (P = 0.947), respectively. One patient receiving a paediatric allograft developed small-for-size liver syndrome post-transplantation. There was no difference in primary non-function, early allograft dysfunction, biliary complications, vascular complications, or infection between the two groups. Conclusion Our study indicates that using paediatric donor livers in well-selected adult recipients is a safe procedure, considering there was no suitable paediatric recipient. However, the risk of portal hyperperfusion should be considered in clinical cases such as size-mismatched transplants.

Purpose Previous studies have demonstrated that let-7e is associated with inflammatory responses. To date, the roles and mechanisms of let-7e have not been completely revealed.Therefore, we aim to identify proteins associated with let-7e overexpression and explore their functions in the immune responses, including in cytokine production. Experimental design High-throughput isobaric tag for relative and absolute quantitation (iTRAQ) technology is used to provide the first genome-wide study of THP-1 cells transfected with let-7e mimic followed by lipopolysaccharide (LPS) stimulation. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway database and KEGG pathway enrichment analyses are used to analyze a large number of differentially expressed proteins (DEPs) associated with let-7e overexpression or LPS stimulation. Quantitative reverse transcription PCR (qRT-PCR) and 50% tissue culture infective dose (TCID50) assays are processed to confirm the relationship of let-7e and dengue virus replication. Results iTRAQ results show that let-7e is associated with the expression of anti-viral proteins. What's more, calcineurin subunit B type 1, an anti-tumor factor, is upregulated by let-7e after LPS stimulation. KEGG analyses identify that some DEPS associated with let-7e overexpression are involved in the measles and influenza A pathways, and LPS-stimulated proteins in THP-1 cells are mainly enriched in transcriptional misregulation in cancer pathway and hippo signaling pathway (multiple species). The results of qRT-PCRand TCID50 show that let-7e promotes dengue virus replication, which is in agreement with the iTRAQ results. Conclusions and clinical relevance These results provide molecular insights into the regulatory mechanisms of let-7e in cytokine expression, virus replication, and anti-tumor function.

543 Background: HER2 targeted therapy has revolutionized the survival outcomes of early and advanced HER2+ breast cancer (BC). However, among HER2+ patients, the therapeutic response to HER2 inhibitors vary. To understand the molecular mechanism of the variability in therapeutic efficacies, the mutational landscape of HER2+ tumors need to be elucidated. Methods: 107 HER2+ Chinese stage I-III BC patients were included in the study, including 64 HR+ and 43 HR- patients. A majority of the patients were diagnosed with infiltrating ductal carcinoma (99/107). Capture-based targeted sequencing was performed using a panel consisting of 520 cancer-related genes spanning 1.64 MB of the human genome. Results: 1,119 alterations were detected, including 478 single nucleotide variants (SNVs), 14 insertions or deletions, 29 fusions, 593 copy number amplifications (CNA), 2 large genomic rearrangements and 3 CN deletions in 267 genes. Alterations in 99 genes were shared between HR+/HER2+ and HR-/HER2+ tumors; while 123 and 45 genes were only detected in either HR+/HER2+ or HR-/HER2+ tumors, respectively. CNA, splice site and frameshift mutations were significantly more in HR+/HER2+ patients ( p= 0.017). Specifically, CNA in SPOP, CCND1, FGF19, FGF3, FGF4, RNF43, RAD51C, ADGRA4 and MDM4 and various alterations in GATA3 were significantly more among HR+/HER2+ tumors ( p< 0.05). In addition to HER2 amplifications, concurrent fusions in ERBB2 (67%, 4/6), SNVs in ERBB3 (100%, 3/3) and ERBB4 (100%, 1/1) were more likely to be detected in HR+/HER2+ tumors, while concurrent EGFR amplifications were exclusively detected in HR-/HER2+ tumors. The trend of concurrent mutations was consistent with mutation types detected in HER2- tumors based on HR status, wherein EGFR amplifications were more frequent in HR-/HER2- tumors, while SNVs in EGFR, ERBB2, ERBB3 and ERBB4 were more predominant in HR+/HER2- tumors. Based on KEGG pathway analysis, HR+/HER2+ tumors had more frequent alterations in TGFb ( p= 0.007), WNT ( p= 0.002) and homologous recombination ( p= 0.004) pathways than HR-/HER2+ tumors. Furthermore, our data revealed that HR+/HER2+ and HR-/HER2+ patients had comparable TMB ( p= 0.24), with a median TMB of 4.0 mutations/Mb for both. Conclusions: Our study revealed genetic heterogeneity between HR+ and HR- HER2+ tumors. The distinct genetic alterations are potentially relevant in the development of optimal treatment strategies for such patients.

579 Background: The standard management of early stage human epidermal growth factor receptor 2 (HER2) positive (+) breast cancer (BC) involves neoadjuvant therapy with combination of chemotherapy and HER2-targeted therapy followed by surgery. However, diverse pathologic responses were observed. We interrogated whether baseline genomic heterogeneity contributes to the varied therapeutic responses. Methods: Capture-based targeted sequencing using a panel consisting of 520 cancer-related genes, spanning 1.6MB of human genome, was performed on tissue biopsy samples, obtained prior to neoadjuvant therapy, of 33 HER2+ women with stage I-III BC. The median age of the cohort was 53. The correlation between genomic alterations and pathologic response were analyzed by multivariate analysis. Results: A majority of them was diagnosed with stage II (67%, 22/33), while 30% (10/33) had stage III and 3% (1/33) had stage I disease. 58% (19/33) were HR+ and 42% (14/33) were HR-. Mutation profiling of baseline samples revealed 349 mutations spanning 145 genes, with TP53, CDK12 and PIK3CA being the top 3 most frequently mutated genes. Neoadjuvant regimen was comprised of trastuzumab and HER2 inhibitor (i.e. pertuzumab or lapatinib). 15 patients used single HER2 inhibitor;18 used dual HER2 inhibitors. Endocrine therapy was also administered to HR+ patients (19/33) in combination with trastuzumab and HER2 inhibitor. Complete pathologic response (pCR) was observed in 45.5% (15/33) of patients. Interestingly, ROS1 copy number amplifications (CANs) were only identified in patients achieved pCR (p = 0.033). In contrast, missense mutations in PIK3CA and CNAs in CCND1, FGF19, FGF3, FGF4, SPOP, HNF1B and BRIP1 showed a trend of being less likely to mutate in pCR patients (p values between 0.05-0.1). Previous reports have suggested that pCR rates in HER2+ patients are associated with HR status. However, our data revealed comparable pathologic response of patients based on either HR status or neoadjuvant regimen. Conclusions: Our data revealed a distinct mutational profile between patients achieved pCR vs patients did not. Further studies with a larger cohort are required to confirm these findings.