Molecular profiles and circulating tumor-DNA detected in Chinese early stage breast cancer.

Abstract

With the development of gene-sequencing technology, genome biomarkers, including Erb-B2 receptor tyrosine kinase 2 (ERBB2), phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha (pIK3CA), BReast CAncer gene 1 (BRCA1), and BReast CAncer gene 2 (BRCA2), and immunomarkers, including the tumor mutational burden (TMB) and programmed death-ligand 1 (PD-L1), have become important in the selection of treatment. Twenty patients with early stage breast cancer who underwent surgery were enrolled in this study. Tissue samples and paired postoperative peripheral blood samples were collected and subjected to the targeted-capture sequencing of 1,021 cancer-associated genes. The most frequently altered genes were tumor protein 53 (TP53; 70%), PIK3CA (40%), protooncogene MYC (35%), ERBB2 (30%), and cyclin-dependent kinase 12 (CDK12; 20%). Six (30%) patients presented with ERBB2 amplification of NGS and simultaneously were positive for human epidermal growth factor receptor 2 (HER2) of IHC. ERBB2 amplification and being HER2 positive were common in breast cancer patients without lymph node metastasis (5/6, 83.3%) and those in stages IA-IIA. Most of the somatic mutations clustered in the TP53 pathway, followed by the PI3K pathway. The TMB was lower than metastatic breast cancer in our cohort, and ranged from 0 to 9.6 mut/Mb (median: 1.92 mut/Mb). Interestingly, more patients had the ERBB2 mutation in the non-lymph node metastasis group than the lymph node metastasis group (55.6% vs. 9.1%; P=0.049). Similarly, more patients had the CDK12 mutation in the non-lymph node metastasis group than the lymph node metastasis group (44.4% vs. 0%; P=0.026). Circulating tumor deoxyribonucleic acid (ctDNA) was detected in 7 of the 20 patients (35%). Of these patients, 71.4% (5/7) were in stage I/II. In addition, no correlation was found between ctDNA detection and clinicopathological features or the driver gene mutations (e.g., PIK3CA and ERBB2). However, patients positive for ctDNA had a higher TMB than those negative for ctDNA when grouped according to the median TMB (1.92 mut/Mb; 85.7% vs. 38.5%; P=0.043). This study described that genomic characteristics of Chinese early stage breast cancer, and the results showed that TMB was related to the detection of ctDNA in postoperative blood.