Abstract 2303: Identifying and stratifying circulating tumor cell cluster subtypes in metastatic breast cancer patients and evaluating their clinical outcomes

Abstract Background: Circulating tumor cell clusters (CTCCs) are aggregated groups of tumor cells that detached from primary tumors and circulate the bloodstream. However, while Circulating Tumor Cells (CTCs) are a well studied phenomenon, CTCCs remain relatively unexplored and ill-defined, with only a few descriptive investigations evaluating their clinical utility. Adding to CTCC complexity is that various subtypes exist, including homotypic clusters consisting of a homogenous population of tumor cells and heterotypic CTCCs made of CTCs with immune/stromal white blood cells (WBCs). Furthermore, CTCs can undergo Epithelial-Mesenchymal Transition (EMT), a process characterized by loss of epithelial traits and upregulation of mesenchymal traits, and can form clustered EMTs (CEMTs). Moreover, CTCs can fuse with macrophages forming Tumor Macrophage Hybrid Cells, aka Cancer-Associated Macrophage Like cells (CAMLs) when in circulation. We enumerated all these types of cells and complex aggregates in the peripheral blood of patients with metastatic breast cancer (mBC). Methods: We enumerated the 6 populations from patient samples enrolled in IRB aproved prospective pilot studies. Whole peripheral blood (7. 5mL) was filtered and stained with cytokeratin (CK) Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 2303.