Cancer has the potential to spread and cause additional tumors to grow in other parts of the body, separate from the original tumor site. When a cancerous tumor grows, it sheds cancer cells into the lymphatic system and into the blood. Many and sometimes all of the cancerous cells that are shed are destroyed by our immune system or by other mechanisms and do not spread.
However, sometimes the cancerous cells do spread. This is why catching cancer at an early stage provides a better chance of cure. As tumors grow in size more and more cells are shed, and once spread to lymph nodes or distant organs has occurred, the chance of cure decreases.
Different tumor types tend to spread to specific lymph nodes and organs. There is no certainty about where any given type of cancer can spread. For the cancer to spread to a particular lymph node or distant organ, a hospitable environment that supports the growth of that particular tumor must exist.
In addition, a set of receptors on normal cells of the distant organ is typically necessary for the cancerous cells to latch onto and take hold. If a cancer spreads to a distant organ, such as a colon cancer spreading to the liver, the cancer is still called colon cancer. It is not then called colon cancer and liver cancer.