How does cancer make you ill?

Cancerous cells divide uncontrollably. On its own a single tumor can make you quite ill, for example by pressing against nerves, blocking the digestive system or blood vessels, or by releasing hormones that can affect the normal workings of your body.

Things can get much worse, however, if the cancer becomes malignant and spreads. This happens when a single cancerous cell breaks away from the main tumor and starts growing and dividing elsewhere in the body. Once a tumor metastasises, it is much more difficult to treat, and can make you much more ill because more areas of the body are affected.