DTC-Flow: a flow cytometry-based detection platform for characterizing bone marrow disseminated tumor cells in breast cancer

The presence of bone marrow (BM) disseminated tumor cells (DTC_bm) identifies early-stage breast cancer patients at increased risk of recurrence and poorer overall survival. However, limitations in detecting DTC_bm by standard immunohistochemical approaches have hampered clinical application. To address this gap, we developed a flow cytometry-based method, DTC-Flow, that enables the sensitive and efficient detection and molecular characterization of breast cancer DTC_bm. Our analysis identified HER2 as a sensitive marker for detecting breast cancer cells, including those lacking HER2 amplification are claudin-low. DTC-Flow using a HER2/EpCAM/CD45 marker panel enabled >90% cancer cell recovery and sensitivity of one cancer cell per million nucleated BM cells across a range of breast cancer subtypes. Molecular analyses of DTC-Flow-sorted DTC_bm from metastatic patients suggested a quiescent state and demonstrated their close genomic relationship to primary/metastatic tumors, as well as continued genetic evolution. In early-stage breast cancer patients, DTC-Flow detected DTC_bm with greater sensitivity than cytokeratin-based immunohistochemical approaches. Our data support the development of DTC-Flow as a sensitive and specific platform to identify breast cancer patients harboring DTC_bm and better understand the biology of minimal residual disease. Ultimately, this platform could enable the selection of personalized therapeutic approaches based on molecular features of DTC_bm, monitoring of DTC_bm to assess the efficacy of such therapies, and the development of novel therapeutic approaches targeting unique biological vulnerabilities of DTCs in order to eradicate these cells before they can give rise to lethal recurrent cancers.