Background: Liquid biopsy analysis detecting circulating tumor cells (CTC) or circulating tumor DNA (ctDNA) is a non-invasive approach that may provide clinically actionable information for patients’ (pts) treatment decisions when conventional biopsy is otherwise inaccessible or infeasible. Here we report a liquid biopsy analysis method including CTC characterization and ctDNA alterations in late-stage metastatic breast cancers (MBC). Methods: Blood samples were collected for cell and cell-free DNA analysis from 57 pts with MBC. 44 pts were progressing on treatment and 13 were responding to treatment. Blood was also collected from 25 blood donors (HD) with no known cancer history. After plasma isolation, nucleated cells were plated, and slides were bio-banked. Immunofluorescent staining and subsequent imaging were performed on replicate slides. CTCs were identified using Epic Sciences digital imaging and machine learning algorithms trained to identify breast cancer cells. Single-cell (sc) isolation for genomic quantification of large-scale transitions (scLST) was used to further characterize individual CTCs. cfDNA from bio-banked plasma was analyzed using a validated NGS panel to detect class 1A ctDNA alterations. Results: Within this cohort of 57 MBC pts, CTCs, scLST+CTCs and ctDNA alterations were detected in (77%, 49% and 33%, respectively). All MBC pts on active therapy (23%) had no CTC detected. No CTCs, scLST+CTCs or ctDNA were detected in the HD cohort, suggesting high specificity (100%, 100% and 100%, respectively). The presence of CTCs or of scLST+CTCs had low concordance with the presence of ctDNA+ alterations in MBC pts, suggesting that these platforms provide independent and complementary value when identifying MBC. To test this hypothesis, we designed combination models which added ctDNA to cell analysis methods ([CTC+][ctDNA+] and [scLST+CTC+][ctDNA+]). Adding ctDNA to either cell analysis method increased sensitivity by 5% and 12%, respectively, over the individual methods and retained 100% specificity. Conclusions: Here we demonstrate the value of comprehensive cell and cell-free liquid biopsy analysis for the detection of MBC pts. Our data suggest there may be clinical utility of adding cell-free to cell analysis for the identification of MBC. Analysis of the comparative and combined utility of these liquid biopsy methods in earlier settings is ongoing.