Chromosomal instability (CIN) is the most common form of genomic instability in cancer. CIN leads to structural and numerical chromosomal aberrations and to heterogeneity of such aberrations inside the same tumor. Together with other forms of genomic and epigenomic instability, CIN underlies the most dangerous feature of cancer cells, namely, ability to evolve, allowing cancer cells to evade immunologic surveillance, to metastasize, to become resistant to drug treatments. Studies of chromosomal instability are significantly impeded by the lack of comprehensive approaches for simultaneous detection of different forms of ongoing chromosomal instability and their outcomes. We developed an approach that allows to analyze the clonal composition and chromosomal heterogeneity in cell lines and cancer samples, as well as rates of different forms of ongoing chromosomal instability in cancer cell lines. At the heart our analysis is a multiplex interphase FISH (miFISH) with seven sequential hybridizations of color probe panels resulting in the assessment of a total of 35 probes per single cell. Each probe panel is designed to include the centromeric probe and probes on the p- and q-arm for a given chromosome that allows for the simultaneous assessment of centromeric probes and gene-specific arm probes. This approach was applied to interphase nuclei, metaphase spreads and bi-nucleated/dividing cancer cells in colorectal and cervical cell lines and cancer samples. miFISH allows for automated acquisition of nuclei and metaphase spreads on a BioView spotcounting system. A gallery provides detailed views for semi-automatic as well as manual analysis of the obtained images. A total of 10000-25000 cell images were collected from each slide. The simultaneous evaluation of our strategically chosen centromeric and gene-specific probes within the same cells allows unprecedented insights in the patterns of distribution of genetic material among cancer cells in cancer cell population, and, especially, in dividing cells. We evaluated clonality, clonal and non-clonal chromosomal heterogeneity, ploidy distributions, and occurrence of endoreplication. Assessment of dividing cells based on equal or unequal distribution of miFISH centromeric and gene-specific signals allowed to estimate and compare the rates and outcomes of different forms of ongoing chromosomal instability such as structural rearrangements and amplifications, loss of chromosomes or chromosomal fragments in micronuclei, non-disjunctions, grossly asymmetrical cell divisions (including multipolar mitoses). Conclusions: Gradual changes in chromosomal/genomic content of cancer cells occur due to structural rearrangements, losses of chromosomes and chromosomal fragments in micronuclei, and by relatively rare single chromosome non-disjunctions. Grossly abnormal cell divisions (massive non-disjunctions and structural rearrangements) is the main source for the high level of chromosomal abnormalities and aneuploidy in evolved cancer cell populations.

Citation Format: Anna Roschke. Comprehensive analysis of clonality, segregation errors, chromosomal instability and heterogeneity in cancer cell lines and cancer samples reveals that cancer evolution is often promoted by highly aberrant cellular divisions [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Translating Cancer Evolution and Data Science: The Next Frontier; 2023 Dec 3-6; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84(3 Suppl_2):Abstract nr B032.