Abstract 4584: High-definition single-cell analysis of liquid and solid biopsies reveals heterogeneity of circulating tumor cells in metastatic colorectal cancer

Treatment of cancer patients is transitioning to personalized strategies using targeted drugs with the required companion biomarkers. Many current biomarkers are tissue-based, requiring a solid biopsy and limiting sampling frequency. Given this, there is significant interest in determining whether noninvasive, blood-based liquid biopsies, utilizing measurements of factors that exist in the blood such as circulating tumor cells (CTCs), reflect solid tumors and can serve as substitutes for solid tumor biopsies. Colorectal cancer with hepatic metastases (mCRC) is one of very few scenarios where metastatic patients routinely undergo surgical resection, providing an opportunity for accessible tissue and simultaneous blood sampling. We collected blood and tumor touch preparations from patients undergoing resection of CRC with the purpose to determine the correlation of solid biopsies and the liquid phase of solid tumors in the mCRC setting. Samples were processed using the previously described HD-SCA (High-Definition Single-Cell Analysis) workflow for high-resolution imaging and characterization of tumor cells at a single-cell level. Briefly, tumor cells were identified by presence of nuclear stain, pan-cytokeratin, and absence of CD45. The colon-specific marker CDX2 was included as a fourth color for further characterization. Subsets of cells were subjected to copy number variation (CNV) profiling. The comparison of pre- and post-surgery blood samples showed that the concentration of CTCs decreased significantly after surgery. The concentration was markedly higher in patients with synchronous disease undergoing simultaneous resection of the primary tumor, indicating that the presence of CTCs is related to tumor burden. Principal component analysis demonstrated that the CTCs were more similar to the metastatic cells than to the primary colon cells. While protein levels varied between the liquid and solid biopsy cell populations, morphologic parameters including, e.g., cell and nuclear area and roundness, were similar in the two. The intrapatient analysis showed heterogeneous CTC populations, in general with a small subset of cells bearing characteristics more similar to the solid tumor cells than the bulk of CTCs. The presence of subpopulations was further indicated by the CNV analysis, which showed that only a minority of CTCs had genomic rearrangements and that, in contrast to the solid biopsy cells, the rearranged cells were largely nonclonal. Based on the hi