What is CANCER?
The human body is made up of a vast collection of cells and every cell contains 23 pairs of chromosomes. Winding through each pair is a double spiral of DNA molecules, the genetic blueprint for life. Each of these molecules contains numerous numbers of genes.

Almost all our cells need to be replaced regularly. Some cells divide every few hours and are shed after living for only a few days. Others live for years. The process of all divisions and growth are controlled by genes that start and stop the growth process. Some of these growth-controlling genes may undergo changes (mutation) that cause them to malfunction and cell growth is then uncontrolled. Simple overgrowth may lead to harmless benign tumour (not likely to spread). However, some genes in a cell not only induce uncontrolled growth, but also cause the cell to invade and damage surrounding blood vessels, nerves, other body tissues or other parts of the body. The latter process is called metastasis.

Doubling Times
Cancer starts with one abnormal cell. That cell divides and becomes two abnormal cells and then four abnormal cells and so on. Cells divide at various rates called doubling times. Fast growing cancer may double over one to four weeks, while slow growing cancer may double over two to six months. So there is a "silent" period after the cancer has started to grow. There is no lump or mass, and the tumour is too small to be detected by any means now known. After many months or years, the doubling process has occurred about 30 times or so. By then the lump may have reached the size of about 1 cm that can be felt, seen on X-ray etc. With the advent of new technology, smaller tumours can now be detected.

Causes of Cancer
For many cancers, no definite cause is known and there is no single cause. There are, however, 4 groups of aetiological factors we now know:

• Viral Carcinogenesis
  Two DNA viruses, the hepatitis B and human papilloma viruses, are responsible for hepatocellular and cervical cancers respectively. Other common viruses directly linked to human tumours include Epstein Barr virus (EBV), Human Herpes virus, Human Immunodeficiency virus, Herpes Simplex virus.
  
  
• Chemical Carcinogenesis
  Chemical Carcinogenesis is an important cause of cancer and can be implicated by certain lifestyles. For example, cigarette smoking and exposure to chemicals in the community or workplace such as asbestos cause lung cancer, dye causes bladder cancer and benzene causes marrow tumours.
  
  
• Radiation
  Radiation damages cellular contents especially DNA. Radioactive isotopes, X-rays and nuclear waste can cause cancer especially some types of leukemia. The main radiation hazard is sunlight, which causes most of the skin cancers.
  
  
• Hormones
  Different hormones and their related growth factors play a variety of roles in carcinogenesis in a number of malignancies including cancer of the breast, endometrium, prostate, ovary, thyroid, testis and bone. In these sites, the cancer results from excessive hormonal stimulation of relevant target cells.
  
  

Common Cancer