Cancer is caused by accumulated damage to genes. Such changes may be due to chance or to exposure to a cancer-causing substance.
The substances that cause cancer are called carcinogens. A carcinogen may be a chemical substance, such as certain molecules in tobacco smoke. The cause of cancer may be:
· environmental agents
· viral or genetic factors.
We can roughly divide cancer risk factors into the following groups:
Biological or internal factors
Age, gender, inherited genetic defects and skin type
For instance, to radon and UV radiation, and fine particulate matter
Occupational risk factors
Including carcinogens such as many chemicals, radioactive materials and asbestos.
Lifestyle-related factors that causes cancer include:
Tobacco, alcohol, UV radiation in sunlight
Nitrites and poly aromatic hydrocarbons generated by barbecuing food
Source: All about cancer