Circulating free DNA integrity and concentration as independent prognostic markers in metastatic breast cancer.

PURPOSE: Non-invasive blood-based molecular markers have been investigated for cancer diagnosis and prognosis. Circulating free or cell-free DNA (cfDNA) variables have been shown to be putative markers in breast cancer prognosis.

METHODS: Here, we investigated the potential prognostic ability of cfDNA concentration and cfDNA integrity (cfDI) in a study cohort of 268 patients by quantitative PCR. We compared cfDNA concentration and cfDI at baseline and after one cycle of therapy in metastatic breast cancer (MBC) patients.

RESULTS: A significantly increased cfDI (P = 1.21E-7 for ALU and P = 1.87E-3 for LINE1) and decreased cfDNA concentration (P = 1.17E-3 for ALU and P = 1.60E-2 for LINE1) in both repetitive DNA elements after one cycle of therapy was observed. A multiple Cox regression model indicated that cfDI and cfDNA concentration can serve as independent prognostic markers in patients at baseline with HR (95% CI) of 0.70 (0.48-1.01) for ALU cfDI, 0.63 (0.44-0.92) for LINE1 cfDI, 2.44 (1.68-3.53) for ALU cfDNA concentration, and 2.12 (1.47-3.06) for LINE1 cfDNA concentration and after one cycle of therapy with HR (95% CI) of 0.59 (0.42-0.84) for ALU cfDI, 0.51 (0.36-0.74) for LINE1 cfDI, 1.59 (1.31-1.92) for ALU cfDNA concentration, and 1.30 (1.17-1.45) for LINE1 cfDNA concentration, respectively. By comparing integrated prediction error of different models, cfDNA variables were shown to improve the prognostic power of the CTC status.

CONCLUSIONS: We hereby show that cfDNA variables, especially in combination with other markers, can serve as attractive prognostic markers for MBC patients at baseline and during the systematic therapy.