Chromosome missegregation compromises the proliferation capacity of diploid cells, indicating that elevated missegregation rates alone are insufficient to generate viable aneuploid cells. The generation of aneuploid cells with sustained CIN requires both elevated chromosome missegregation rates and additional phenotypic changes that permit propagation of nondiploid cells. [@thompson_examining_2008]

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Multiple lines of evidence establish that chromosome missegregation by itself is insufficient to enable aneuploid cell propagation, as aneuploidy consistently imposes fundamental fitness costs including impaired cell proliferation, altered metabolic properties, and reduced immortalization capacity across diverse experimental systems. The mechanistic basis for this constraint appears to involve pleiotropic cellular stress arising from chromosomal imbalance, which must be overcome through additional genetic alterations such as Stat1 inactivation combined with Myc activation to suppress immune infiltration and enable tumor progression. While elevated merotely can experimentally induce chromosomal instability in otherwise stable near-diploid cells, demonstrating that missegregation mechanisms are sufficient to generate aneuploidy, the observation that even chromosomally unstable lymphomas converge on specific recurrent chromosome gains suggests that ongoing missegregation is counteracted by strong selection pressures favoring particular karyotypes. What remains contested is the dual role of aneuploidy itself, which paradoxically drives spontaneous tumor formation in aged animals while simultaneously suppressing chemically or genetically induced tumorigenesis, indicating that the relationship between chromosome missegregation, resulting aneuploidy, and cellular fitness depends critically on cellular context and cooperating genetic changes.

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