Most of the time, we don’t know exactly what causes any particular cancer, but we do know some of the risk factors for cancer. Having a particular risk factor doesn’t mean that you will definitely get cancer.
Some risk factors are very likely to cause cancer, whereas others will only slightly increase the risk of getting it. Usually cancer is the result of a combination of several risk factors.
Having a particular risk factor for cancer doesn’t mean that you will definitely get cancer – just as not having it doesn’t mean that you won’t.
Smoking is a good example of this. If you smoke, it isn’t certain that you will get lung cancer – just as if you don’t smoke, it’s not certain that you won’t. But smoking will greatly increase your risk of getting lung cancer. About 9 out of 10 people who develop lung cancer are smokers.
For most people, increasing age is the biggest risk factor for developing cancer. In general, older people (those over 65) are far more likely to develop cancer than younger people (those under 50).
Cancer is very common. Most of us have relatives who have had cancer. Some people worry that a history of cancer in their family greatly increases their risk of developing it. But, in fact, fewer than 1 in 10 cases (5–10%) are associated with a strong family history of cancer.