Circulating Clusters In Breast Cancer Express Cancer Stem Cell Phenotypes

Breast cancer is a leading cause of death in women and its metastatic spread to distant organs is responsible for over 90% of these deaths. Circulating tumor cells (CTCs) implicated in the metastatic process occur when cancer cells undergo cytoskeletal and phenotypic transitions that enhance motility, then penetrate into the blood circulation. While CTC dissemination has typically been considered as the spread of single cells, recent evidence suggests that collective migration results in polyclonal circulating clusters that are the main drivers of metastasis. To study circulating clusters we have developed a dual microfiltration system employing two stages of antigen-independent mechanical cell isolation. As whole blood is passed through the system, circulating clusters are trapped by the first stage while single CTCs are retained by the second stage. Characterization experiments using cell lines demonstrated a capture efficiency of 87.1% for clusters and 85.7% for single cells on their respective microfilters. This system was used to investigate circulating cells in the metastatic MMTV-PyMT syngeneic mouse breast cancer model. Both clusters and single CTCs were detected in mice with histological evidence of lung metastases (14-16 weeks old), but not in mice that had not yet developed metastatic tumors ( 50% of circulating clusters. The presence of cancer stem cells was correlated to cluster size, with smaller clusters containing a greater percentage of CD90+/CD24+ cells. Isolated clusters will be further analyzed to quantify expression levels of cancer stem cell markers in each individual constituent cell. The analysis of circulating clusters may provide crucial insight into the mechanisms of metastatic disease and provide the means to discover novel targets for therapeutic intervention. Citation Format: Ramdane Harouaka, Gabrielle Hodges, Allison David, Rishika Polasani, Spencer Freeman, Katherine Sanchez, Kaitlin Harvey, Max S. Wicha. Circulating clusters in breast cancer express cancer stem cell phenotypes [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4776. doi:10.1158/1538-7445.AM2017-4776