The human body is made up of hundreds of different types of cell, all of which behave differently. A cell in the kidney, although it contains the same genetic information as a brain cell, performs a completely separate role.
Cancer happens when a tiny part of the cell's mechanism goes wrong. And just as there are hundreds of types of cell, there are hundreds of types of cancer, none of which can be treated in the same way. It is the nature of cells to divide and increase their number in a process called mitosis. Normal cells divide to replace those lost, or to repair injuries only, then stop dividing.
Cancer is an abnormal, continuous multiplying of cells. The cells divide uncontrollably and may grow into adjacent tissue or spread to distant parts of the body. The mass of cancer cells eventually become large enough to produce lumps, masses, or tumours that can be detected, which can be benign or malignant:
benign tumours:
are not cancerous
can usually be removed
do not come back in most cases
do not spread to other parts of the body, and the cells do not invade other tissues
malignant tumours:
are cancerous
can invade and damage nearby tissues and organs
metastasize (cancer cells break away from a malignant tumour and enter the bloodstream or lymphatic system to form secondary tumours in other parts of the body)
The smallest cancer that can be detected by examination, x-ray, or scan is slightly less than 0,5 to 1,5 centimetre in diameter and contains between a million to a billion cancer cells.
The malignant tumours are made up of cells that can spread to and damage other parts of the body like bones (back or hips), the lungs, the liver and sometimes the brain. However, only one place is usually affected.
What happens if the cancer spreads?
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 metastasis, and once other organs are involved, then any symptoms of the cancer can get worse. Sometimes it can happen before the patient notices the first symptoms.
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.
