2n or not 2n: Aneuploidy, polyploidy and chromosomal instability in primary and tumor cells

Mitotic defects leading to aneuploidy have been recognized as a hallmark of tumor cells for over 100 years. Current data indicate that ∼85% of human cancers have missegregated chromosomes to become aneuploid. Some maintain a stable aneuploid karyotype, while others consistently missegregate chromosomes over multiple divisions due to chromosomal instability (CIN). Both aneuploidy and CIN serve as markers of poor prognosis in diverse human cancers. Despite this, aneuploidy is generally incompatible with viability during development, and some aneuploid karyotypes cause a proliferative disadvantage in somatic cells. In vivo, the intentional introduction of aneuploidy can promote tumors, suppress them, or do neither. Here, we summarize current knowledge of the effects of aneuploidy and CIN on proliferation and cell death in nontransformed cells, as well as on tumor promotion, suppression, and prognosis.