My father had colon cancer at a very young age. Because of this I am going to have a colonoscopy in a few weeks. Colon cancer is certainly a cancer that can be stopped before it becomes serious. All that needs to be done is finding a polyp and removing, but if a polyp is not found due to not have a colonscopy, then you can have colon cancer.
In recent years genetic testing as become a tool that parents can use to determine if their sons or daughters are more susceptible to certain types of cancers. However, it is important to remember that even if you test negative for a certain disease, the risk does not go away.
A year or so ago my father can genetic testing done on him to determine the likelihood of his children to develop colon cancer. Even though the tests results did come back negative, I still have a higher risk of developing colon cancer.
The Mayo Clinic offers a lot of advice surrounding genetic testing. To view their thoughts and suggestions click here
http://www.mayoclinic.com/health/genetic-testing/CA00088