How can one prevent cancer?

Cancer is a deadly disease that has no cure. Those who suffer from it are doomed to die. People who are diagnosed with cancer go through a depressive phase as it means that their life has come to an end. It is better to treat if it is diagnosed at an early stage.
Cancer is caused due to genetic and environmental factors. Many people feel that they need not take the necessary precautions as many are hale and hearty despite their risky habits. Some perhaps may have all the habits that are cancer causing, but yet they remain free from the disease. On account of this many feel that cancer just happens and environmental factors may not necessarily cause it. Nevertheless, scientists feel otherwise and feel required precautions need to be taken to prevent the disease.