In addition, the cancer may not follow the usual instructions that keep cells spaced out properly. As the cells are being made much more often than healthy cells, the cancer cells can form a growing lump in the body called a tumour or a lesion. As it gets larger, it can even grow its own vessels to keep it supplied with blood. A benign, or non-cancerous tumour shares this uncontrolled growth, but will not generally invade neighbouring tissues and damage them. The type of cell in which the cancer starts will generally determine the speed at which it grows, and its resistance to treatment, although there are many variations.
Cancers harm health in a number of ways.
The very size of the tumour can interfere with nearby organs, or ducts which carry important chemicals, causing pain or other symptoms. For example, a tumour on the pancreas can grow to block the bile duct, leading to the patient developing obstructive jaundice. 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.