Chromosomes are threadlike structures present within the nuclei of cells.
DNA's double helix structure allows the chromosomes to be replicated during cell division. Certain genes called tumor suppressors slow down the process of cell division, causing cells to die. Changes in DNA can sometimes cause normal cells to become cancerous by de-activating the tumor suppressor genes. Researchers are still investigating how and why some genes mutate but have discovered that inherited DNA changes may cause cancers to occur more frequently in some families. In 1994, researchers discovered that women who carry mutations of BRCA1 or BRCA2 are at higher risk of developing both breast and ovarian cancer than women who do not have these genetic mutations.