Circulating blood microbiome biomarkers as liquid biopsy in breast cancer
TL;DR
The findings support liquid microbiopsy as a complementary extension of liquid biopsy but must be considered as exploratory, and warrant multicenter validation in larger independent cohorts with standardized pre-analytics and low-biomass controls.
Abstract
Circulating tumor material can already be used to help in cancer management, but host–microbiota interactions may add complementary value. This study evaluated a “liquid microbiopsy”, combining cell-free microbial DNA (cf-mbDNA) with host biomarkers of microbial translocation/permeability (LBP, sCD14, I-FABP), to refine staging and prognosis in breast cancer. We analyzed 136 individuals: 58 metastatic breast cancer (MBC), 58 early breast cancer (EBC), and 20 healthy donors. Plasma cf-mbDNA was quantified by 16S rRNA qPCR with extraction/run negative controls; LBP, sCD14, I-FABP by ELISA; and CRP by immunoturbidimetry. Circulating tumor cells (CTCs) and PD-L1 on CTCs were assessed by CellSearch® and immunostaining. Diagnostic performance was assessed by area under the ROC curve. In MBC, progression-free survival (PFS) and overall survival (OS) were analyzed using Kaplan–Meier and Cox models. LBP discriminated EBC from MBC with an AUC 0.92, with a slight improvement in the 3- or 5-marker models (AUC 0.936–0.939). For EBC vs healthy donors, CRP showed modest performance (AUC 0.73), and marker combinations offered no improvement.. In MBC (median follow-up 77.5 months), median PFS and OS were 4.5 and 14.5 months, respectively. In univariate analysis, shorter PFS was associated with tumor subtype, > 3 prior treatments, > 2 metastatic sites, CTCs ≥ 5, and PD-L1–positive CTCs detection. In multivariate analysis, sCD14 and I-FABP independently predicted PFS, while sCD14 was independently associated with OS. A measurable host–microbiota–barrier axis (LBP, sCD14, I-FABP) provided stage-related and prognostic information complementary to CTC/PD-L1 status, whereas cf-mbDNA load alone showed limited discriminative value. These findings support liquid microbiopsy as a complementary extension of liquid biopsy but must be considered as exploratory, and warrant multicenter validation in larger independent cohorts with standardized pre-analytics and low-biomass controls. NCT03449264; NCT02866149.