Assessment of basal-like breast cancer by circulating tumor DNA analysis

Standardized methods for the detection and assessment of circulating tumor DNA (ctDNA) in breast cancer are not sufficient. In the present study, the method and the potential application of ctDNA in the diagnosis of breast cancer were explored. DNA was extracted from the tumor tissues, plasma and peripheral blood cells of 11 patients with early-stage invasive breast cancer. Primers were designed against the exons of phosphatidylinositol-4,5-biphosphate 3-kinase catalytic subunit α, p53, epidermal growth factor receptor, Akt and phosphatase and tensin homolog. The amplicon-based method for whole-exon sequencing was performed. The associations between the ctDNA mutant frequency with the tumor DNA mutant frequency, and the ctDNA concentration with clinical data were analyzed. A linear association was identified between the concentration of ctDNA and the tumor volume for the 3 patients with basal-like breast cancer, and not in other subtypes. The mutation frequency differed the least between ctDNA and tissue DNA in basal-like breast cancer. ctDNA retained the constituent ratio of gene mutations identified in the corresponding tumor tissue. The ctDNA detection rate depended to a certain extent on the mutation frequency in tumor tissue; for example, a mutant locus with a mutation frequency of >30% in tissues presented a detection rate of >40% in plasma samples, whereas a locus with a mutation frequency of <10% in tissue was associated with a detection rate of ≤1% in the plasma. Therefore, ctDNA may reflect the mutations observed in cancer. Compared with other subtypes, ctDNA may be a more sensitive biomarker for the assessment of mutation and cancer burden in basal-like breast cancer relative to other subtypes.