And a brain tumour can push on important parts of the brain, causing blackouts, fits and other problems. Even benign tumours can cause these problems if located in the wrong place. When a cancer invade nearby tissues, they can cause bleeding from damaged blood vessels, and stop the organ which they are invading from working properly. As a tumour grows, cells can break off and start growing on adjacent tissues and organs. For example, if a bowel cancer has spread through the wall of the bowel itself, it can start growing on the bladder.
Cells can also enter the bloodstream and travel to distant organs, such as the lungs or brain.
When new growths form on these organs, they behave like the original tumour - so bowel cancer cell in the lung will not be lung cancer. This process of spreading is called metastesis, and once other organs are involved, then any symptoms of the cancer can get worse. However, it may be some time before a growing cancer in certain parts of the body produces symptoms that the patient can notice. Once a cancer has started to spread beyond its original site, then the chances of a cure begin to fall, as it becomes more difficult to treat. There are three principal ways of treating cancer.