When cancer spreads in the body, it is first and foremost due to changes, or mutations, in the DNA of cells. Because of a mutation or other abnormality in a cancer cell's genome (the DNA stored in its nucleus), the cell may become separated from its neighbors and invade surrounding tissue.

How does cancer develop and spread?

Cancer is a disease caused when cells divide uncontrollably and spread into surrounding tissues. Cancer is caused by changes to DNA. Most cancer-causing DNA changes occur in sections of DNA called genes. These changes are also called genetic changes.

Where is cancer most likely to spread?

The lungs. The lungs are the most common organ for cancers to spread to. This is because the blood from most parts of the body flows back to the heart and then to the lungs. Cancer cells that have entered the bloodstream can get stuck in the small blood vessels (capillaries) of the lungs.