- The word ‘cancer’ comes from the Latin for ‘crab’. Cancer can be described as a group of diseases in which cells grow uncontrollably and have the ability to spread away from the site of origin. Cancer is actually not one disease as there are more than 100 different cancers. Each type of cancer has its own characteristics. When a cancer spreads to another part of the body it takes its own characteristics with it. So, for example, if a renal cancer spread to the liver the tumour in the liver would both look and behave the same way as the original tumour. This is how primary tumours that have not been located can be found by examining the secondary tumour. Cancer cells develop as a result of damage to DNA, the controlling mechanism for all the activities of the cells. This damage may be caused by a multitude of factors, including environmental, dietary and genetic. The body normally repairs damaged DNA, but in cancer cells this does not occur.
- It is now believed that cancers originate from a single cell. This cell divides and eventually forms what we would class as being a tumour. However, tumours are also heterogenic, which means the cells within the tumour differ genetically from each other and have collected varying genetic mutations as they have divided. For a tumour to be recognised by either clinical or radiographic examination it is likely to contain about 1 billion cells.
- Cancerous tumours are known as malignant tumours. Malignant tumours have a number of characteristics different from those of normal cells. The rate of cell division in cancer cells is greater than the rate of cell death. This is in contrast to normal cells where the number of cells produced equals those dying. Cancers do not always grow particularly fast. It is actually the lack of cell death in cancers that causes them to grow rather than the speed of cell division being particularly fast. Another important characteristic of cancer cells is their inability to recognise when they come into contact with different cell types. Malignant tumours invade and destroy surrounding tissues and are metastatic, initiating the growth of similar tumours in distant organs. They are able to spread away from the site of origin via the blood stream or the lymphatic system.
- Cancerous tumours can originate in any of the common tissue types in the body. Contrary to popular belief it is only tumours that arise in epithelium such as renal cancers that are termed “carcinomas”.
- Not all tumours are malignant; tumours can be benign. A benign tumour is a non-malignant abnormal mass of tissue that is restricted to a limited area (localised). The cells in a benign tumour are derived from normal cells, but undergo changes that make them unresponsive to the controls that limit growth.
- The benign tumour may form a capsule of connective tissue around itself that separates the tumour from adjacent normal cells therefore pushing aside normal tissue but not invading it. A benign tumour does not attempt to spread away from the site of origin. They are not metastatic; that is, they do not form secondary tumours in other organs.
