Tobacco products have been identified as mutagens. However, some tobacco users develop cancer and some do not. The reason for this apparent inconsistency is

some people are more predisposed to developing cancer when exposed to mutagens

Explanation:

Cancer predisposition is a term that means that an individual is more likely to develop cancer during his or her life due to genetic and other factors. Usually these individuals have relatives who have had some form of cancer and know that there is a greater possibility that they have too. This is not to say that cancer-prone individuals will have cancer someday, only that the chances of getting the disease are higher.

People predisposed to cancer are more likely to develop cancer when exposed to mutagens and this is a likely reason to explain why some tobacco users develop cancer and others do not.

The functions of the specific persons body