Cancer cells are notorious for their genetic disarray. A tumor cell can contain an abundance of DNA mutations and most have the wrong number of chromosomes. A missing or extra copy of a single chromosome creates an imbalance called aneuploidy, which can skew the activity of hundreds or thousands of genes. As cancer progresses, so does aneuploidy. Some advanced tumors can harbor cells that have accumulated more than 100 chromosomes, instead of 46 in normal cells.