Most mutations that cause cancer occur within body cells, and body cell mutations are not inherited. If cancer is not inherited, why does cancer statically appear to run in families? Family members have a similar genetic make-up that may make them predisposed to cancer.
Family members are exposed to similar environmental conditions.
Family members have a widely varied genetic make-up that can be affected by specific mutagens.
Family members share the contagious mutagens that can be passed by close exposure.

Family members have a similar genetic make-up that may make them predisposed to cancer.

Explanation:

Variation in certain genes can increase the risk of developing certain cancers. This is why certain cancers run in families. There are lots of examples where the risk factor is small, but in some cases, the risk factor is very large.

For example, mutations in BRCA1 are very highly linked to the risk of breast cancer. As a result, many women with mutations in this gene opt to get a mastectomy to reduce their chances of developing breast cancer.

answer; i believe the answer is (polygenic inheritance;

"1. it should be, it has been for about 20 years, and it's really not much different in the end than breeding animals to have particular traits. there are always concerns about genetically engineered animals/plants affecting the environment in unexpected negative ways, but i can't think of an example where the fears didn't turn out to be baseless.  

first, as you point out, it would be a great advance in pharmacology, to be able to tailor drugs and their doses to me. the pros involve better medical treatment. the cons involve privacy issues like insurance companies denying coverage to people with genetic risk factors. looking at dna markers wouldn't affect the frequency of genetic diseases, but it would allow detection of them earlier. and ok, actually i suppose that if people used this information to avoid having children with genetic diseases, some might decrease in frequency."