What is Cancer?
Cancer is a term used to describe a disease of the body's cells where cells divide abnormally, without control and are then able to invade other tissues via the blood or lymph systems. Cancer is not a single disease with a single cause and a single type of treatment. There are more than two hundred types of cancer which are generally named after the organ, or type of cell from which the tumour originates - For example, a primary cancer that starts in the breast is called breast cancer.
Cancer types can be classified into broader categories:
- Carcinoma - cancer that arises from the lining cells of the body's inner surface (lungs, bowel, reproductive organs etc.).
- Sarcoma - cancer that originates in the connective or supportive tissue. These are the cells that make up bone, cartilage, fat, muscle and blood vessels.
- Leukaemia - cancer that starts in blood forming cells such as bone marrow and spleen, which causes large numbers of white blood cells to be produced and enter the blood.
- Lymphoma and myeloma - cancers that originate in the cells of the immune system.
- Central Nervous System cancers - cancers that originate in the tissues of the brain and spinal cord.
Normally, cells grow and multiply in an orderly way with the process of old cells being replaced with new cells to maintain healthy tissues and repair injuries. However, in some cases this process goes awry with the genetic material of cells becoming damaged and producing mutated cells. Therefore old cells do not die and the body still produces new cells resulting in an uncontrolled growth to form a cellular mass called a tumour.
There are two types of tumours:
- Benign tumours are not cancerous but can be dangerous if they press on vital organs, as the brain. They can often be removed and in most cases, they will not recur. Benign tumours do not spread to other parts of the body.
- Malignant tumours are cancerous. Cells in these tumours can invade nearby tissues and spread to other parts of the body.
As mentioned, cancer cells can spread to other parts of the body from the original cancer site through the blood or lymphatic system as listed below:
- Invasion - refers to the direct migration and penetration by cancer cells into neighbouring tissues.
- Metastasis - refers to the ability of cancer cells to penetrate into lymphatic and blood vessels, circulate through the bloodstream, and then invade normal tissues elsewhere in the body.