genomic instability

Genomic instability is what happens when a cell's quality-control system breaks down and errors start piling up far faster than normal. Think of a copy shop whose proofreaders have quit: every new copy carries more typos than the last, and the mistakes spread through everything the shop produces. In a cell, those mistakes are mutations and chromosome changes.

More formally, genomic instability is an elevated rate of acquiring genetic alterations, ranging from single-letter mutations to large gains, losses, and rearrangements of whole chromosomes. It usually arises when the genes that copy and repair DNA, or that segregate chromosomes during division, are themselves damaged, removing the safeguards that normally keep the genome stable.

It is considered an enabling characteristic of cancer because it speeds the accumulation of the driver mutations a tumor needs. A genome that changes quickly also generates the variety on which clonal evolution acts, helping tumors adapt and resist treatment. It is both a cause and a consequence within the spiral of cancer progression.