Normally, cells grow and divide to form new cells. When these cells become old or damaged, they die and are replaced by new cells. This process is controlled by genes. However, sometimes, this orderly process does not occur. Old and damaged cells do not die, and new cells continue dividing even when the body does not need them. As a result, a mass of tissue—a ‘tumour’ or ‘lump’—is formed.
This tumour or lump can be benign or malignant. Benign tumours are not cancers, while malignant tumours are made of cancer cells. Benign tumours usually grow slowly and do not spread to other parts of the body, while malignant tumours grow more quickly and invade adjoining parts of the body or spread to other organs. A cancer cell is a cell with the ability to grow out of control and invade other tissues. In most cases, cancer cells form a tumour; however, in some cases, such as leukaemia, there may not be any tumour. In this book, only malignant tumours or cancers are discussed.
Cause of Cancer
The exact cause of cancer is unknown. What is known is that cancer is caused by damage to the genes that control cell division and growth. All cancers are genetic because they are caused by abnormal genes. This damage to genes is a result of interactions between a person’s genetic factors and external factors, including:
- physical agents, such as ionising radiation
chemical agents, such as tobacco smoke
biological agents, such as infections from bacteria and viruses.
Ageing is another factor for the development of cancer. The risk of cancer increases dramatically with age, which is most likely due to a build-up of risks for those cancers that increase with age.
Spread of Cancer
Cancer spreads in three ways:
- local spread: cancer invades the surrounding normal tissue
through lymph vessels: cancer invades the lymph system and travels through the lymph vessels to other parts of the body
through blood vessels: cancer invades the capillaries and veins and travels through the blood vessels to other parts of the body.
Primary and Secondary Malignant Cancers
The location where cancer cells first develop is the ‘primary’ cancer. When these primary cancer cells break away and are carried in the blood or lymph vessels to other parts of the body, this is ‘secondary’ or ‘metastatic’ cancer. This process is called ‘metastasis’. For example, breast cancer can spread to the bones when it is metastatic breast cancer. Metastatic or secondary cancers contain original cancer cells.
Types of Cancer
There are many types of cancers. These are named after the cells or tissues in which they began. Some types of cancers are as follows:
- Carcinomas: these begin in the lining of internal organs or the skin.
Examples are squamous cell carcinoma (SCC) and adenocarcinoma.
Almost 85% of all cancers are carcinomas.
- Sarcomas: these begin from connective tissues that support the body organs, such as the bones, cartilage and tendons. An example is osteosarcoma.
Leukaemia: this arises from blood cells.
Lymphomas: these arise from lymph tissues.
Genetic and Inherited Cancer
All cancers are genetic because cancer is caused by abnormal genes. When a damaged gene is passed from one generation to another, it is said to be inherited. For example, FAP and hereditary breast and ovarian cancer are inherited cancers. Only a very small percentage of cancers (five to 10%) are inherited.
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