Digital Pathology Slides-based Measurement of Tumor Cells and Lymphocytes Within Cytology Samples Supports the Relevance of the Separation by Size of Nonhematological Tumor and Hematological Nontumor Cells in Liquid Biopsies

Abstract

Filtration by size is one method used to study circulating tumor cells in blood samples. Filtration-migration ability is highly dependent of the size of cell nucleus. This implies to search for the appropriate nucleus size able to separate between hematological nucleated and nonhematological nucleated blood cells to maximize circulating tumor cell isolation. Digitalized cytology slides [May-Grünwald Giemsa (MGG) stained and immunocytochemistry (ICC) slides] from various cancer metastases served for manual measurements of nuclei about tumor cells and adjacent lymphocytes to determine the diameters the more able to separate between tumor cells and lymphocytes. Among 2022 cells analyzed (1067 tumor cells and 955 lymphocytes) on MGG stained slides, the mean diameter of tumor cells nuclei was 14.77 µm whereas the mean diameter of lymphocytic nuclei was 6.47 µm (P<0.001). In ICC slides, about 6583 cells (4753 tumor cells and 1830 lymphocytes), the mean diameter of tumor cells nuclei was 9.28 µm whereas the mean diameter of lymphocytic nuclei was 4.95 µm (P<0.001). Areas under the receiver operating characteristic curves analyses concluded that diameters of 9.37 µm and 6 µm separated the best between tumor cells and lymphocytes in MGG and ICC slides, respectively. Measuring manually the diameters of the smallest tumor cells in ICC slides, we established more than 99% of tumor cells had diameters superior to 8 µm. The sizes differences between tumor cells and lymphocytes support the relevance of the filtration by size to isolate blood circulating nonhematological tumor cells. The existence of small tumor cells with sizes overlapping with those of lymphocytes is worth to optimize the threshold to separate between tumor cells and hematological cells.