biostudies-literatureHiga NBreast Cancer Research Foundation (BCRF)U.S. Department of Health & Human Services | NIH | National Cancer Institute (NCI)309https://www.ebi.ac.uk/biostudies/studies/S-EPMC12290075biostudies-literatureUnknown5(1)<h4>Background</h4>Heterogeneous circulating tumor cells (CTCs) have been implicated in the formation of new metastases. However, circulating cells expressing both tumor and immune cell proteins are often dismissed as insignificant findings in CTC studies.<h4>Methods</h4>Two non-contemporaneous blood samples from a metastatic breast cancer patient were analyzed using an enrichment-free platform to identify canonical, epithelial-only CTCs (CD45-/cytokeratin + , epi.CTCs) and CD45 + /cytokeratin+ immune-like CTCs (im.CTCs). Single cells from both samples were subjected to copy number and protein expression profiling. A cohort of 36 metastatic breast cancer patients was then analyzed to search for additional cases with im.CTCs.<h4>Results</h4>Here, we identified and characterized a populationCommunications medicineSimultaneous expression of epithelial and immune cell markers in circulating tumor cells identified in patients with stage 4 breast cancer.PMC12290075BCRF-16-1895P30CA014089-40BCRF-18-089Hicks JKolatkar ARiker AITafra LLimb ARivera ATweed CKShriver CDNevarez RLee YHiga NHennes VKuhn PPerkins JGfalseSimultaneous expression of epithelial and immune cell markers in circulating tumor cells identified in patients with stage 4 breast cancer.<h4>Background</h4>Heterogeneous circulating tumor cells (CTCs) have been implicated in the formation of new metastases. However, circulating cells expressing both tumor and immune cell proteins are often dismissed as insignificant findings in CTC studies.<h4>Methods</h4>Two non-contemporaneous blood samples from a metastatic breast cancer patient were analyzed using an enrichment-free platform to identify canonical, epithelial-only CTCs (CD45-/cytokeratin + , epi.CTCs) and CD45 + /cytokeratin+ immune-like CTCs (im.CTCs). Single cells from both samples were subjected to copy number and protein expression profiling. A cohort of 36 metastatic breast cancer patients was then analyzed to search for additional cases with im.CTCs.<h4>Results</h4>Here, we identified and characterized a population2025-01-01T00:00:00Z2025 Jul2026-03-15T17:17:49.942Z2025-08-13T03:04:38.363ZS-EPMC122900754070777110.1038/s43856-025-01024-0