Definition

Having an abnormal number of chromosomes that deviates from the typical diploid complement.

A condition characterized by an abnormal number of chromosomes, either more or fewer than the normal diploid number.

Synthesis

Aneuploidy, consistently defined across sources as an abnormal chromosome number that deviates from the normal diploid or euploid state, imposes fundamental cellular costs through multiple mechanistic pathways. The condition creates a proteotoxic burden because proteins encoded by genes on duplicated chromosomes increase approximately twofold in abundance, disrupting stoichiometric balance in protein complexes and triggering widespread metabolic alterations, cell cycle defects, proliferative disadvantages, and heightened sensitivity to protein synthesis interference—effects remarkably consistent regardless of which specific chromosome is gained. However, the relationship between aneuploidy and cancer remains contested, with evidence showing it both drives spontaneous tumor formation in aged animals and simultaneously inhibits chemically or genetically induced tumorigenesis, revealing context-dependent oncogenic and tumor-suppressive roles. Recent work has begun to resolve this paradox by demonstrating that aneuploid cancer cells must actively suppress immune surveillance through specific mechanisms such as Stat1 inactivation combined with Myc activation, suggesting that the fitness costs of aneuploidy create immunogenic stress that cells must overcome to achieve malignancy, though the precise mechanisms linking chromosomal instability to ongoing aneuploidy generation in most tumor cells remain incompletely understood.