Detection of TP53/PIK3CA Mutations in Cell-Free Plasma DNA From Metastatic Breast Cancer Patients Using Next Generation Sequencing

Background Circulating tumor DNA (ctDNA) within a liquid biopsy is a promising marker for genotyping metastatic tumors. Materials and Methods We performed next generation whole exon sequencing of TP53 and PIK3CA genes, which are the 2 most common genetic alterations in breast cancer, in plasma DNA (pDNA) of 17 metastatic breast cancer (MBC) patients and in tumor DNA (tDNA) from their primary tumors. Results We identified 11 mutations (6 in TP53 and 5 in PIK3CA) in tDNA from 8 patients (47%) and 13 mutations (6 in TP53 and 7 in PIK3CA) in pDNA from 7 patients (41%). Six mutations in pDNA were also identified in tDNA but seven were not. Six MBC patients with TP53 and/or PIK3CA mutations in pDNA had a significantly worse survival rate (P < .05) after recurrence than that of the other 8 MBC patients without these mutations. Carcinoembryonic antigen and cancer antigen 15-3 levels did not correlate with prognosis (P = .675 and P = .877, respectively). Conclusion These results suggest that mutations in ctDNA can be detected with next generation sequencing in MBC patients and could be a more useful prognostic factor for survival after recurrence than conventional tumor markers.