Genomic Characteristics and Its Therapeutic Implications in Breast Cancer Patients with Detectable Molecular Residual Disease.

Purpose:Molecular residual disease (MRD) is the main cause of postoperative recurrence of breast cancer. However, the baseline tumor genomic characteristics and therapeutic implications of breast cancer patients with detectable MRD after surgery are still unknown. Materials and Methods:In this study, we enrolled 80 patients with breast cancer who underwent next-generation sequencing (NGS)-based genetic testing of 1,021 cancer-related genes performed on baseline tumor and postoperative plasma, among which 18 patients had detectable MRD after surgery. Results:Baseline clinical characteristics found that patients with higher clinical stages were more likely to have detectable MRD. Analysis of single nucleotide variations and small insertions/deletions (SNV/Indel) in baseline tumors showed that somatic mutations in MAP3K1, ATM, FLT1, GNAS, POLD1, SPEN, and WWP2 were significantly enriched in patients with detectable MRD. Oncogenic signaling pathway analysis revealed that alteration of the Cell cycle pathway was more likely to occur in patients with detectable MRD (p=0.0125). Mutational signature analysis showed that defective DNA mismatch repair and activation-induced cytidine deaminase (AID) mediated somatic hypermutation (SHM) were associated with detectable MRD. According to the OncoKB database, 77.8% (14/18) of patients with detectable MRD had U.S. Food and Drug Administration-approved mutational biomarkers and targeted therapy. Conclusion:Our study reports genomic characteristics of breast cancer patients with detectable MRD. The Cell cycle pathway, defective DNA mismatch repair, and AID-mediated SHM were found to be the possible causes of detectable MRD. We also found the vast majority of patients with detectable MRD have the opportunity to access targeted therapy.