What is cancer?
Cancer is a disease which affects the cells in the body. The body continuously produces new cells which help us heal from injuries, help replace any old body tissues, and which help us to grow. The cells in the body usually multiply and die in an organised manner, such that every new cell replaces a dead cell.
There are however times, when the cells become abnormal and keep growing. Cancer occurs when the cells grow and divide uncontrollably, without dying.
One of the reasons why cancer develops, is because of changes in the DNA inside our cells. The DNA is a chemical in our cells that make up our genes. The genes in turn, are responsible for the functioning of our cells.
The genes that help the cells grow, divide and stay alive, are called oncogenes, while genes that help to ensure cells divide in a controlled manner or die at the right time, are called tumour suppressor genes. Cancers may occur when there are DNA mutations or changes, which turn on oncogenes or turn off tumour suppressor genes, resulting in the cells growing out of control.
When the cells grow out of control, they form a mass or lump called a tumour. A tumour can be benign or malignant.
In a benign tumour, the cells grow slowly and do not normally spread to other parts of the body. Benign tumours are not cancerous.
Malignant tumours are cancerous cells. They spread by invading nearby tissues, and by moving through the bloodstream or lymph vessels to other parts of the body.
This describes cancer that has spread from the part of the body where it started (the primary site), to other parts of the body. When cancer cells break away from a tumour, they can travel to other parts of the body through the bloodstream, or the lymph system.
When the cancer cells travel through the lymph system, they may end up in lymph nodes (small, bean-sized collections of immune cells), or other organs in the body. In many instances, the cancer cells travel through the bloodstream to other parts of the body. Many of these cells die, but some may settle in a new area, start to grow, and form new tumours. This spread of cancer to a new part of the body is called metastasis.
When metastasis occurs, the cancer is named after the part of the body where it started. For instance, breast cancer that has spread to the lungs is called “metastatic breast cancer to the lungs”, not lung cancer.
Treatment is also based on where the cancer started. For example, colon cancer that has spread to the liver is treated as metastatic colon cancer, not liver cancer.