[pfisherman]

The sci-fi use case is that an prognostic / diagnostic / active learning agent pulling information from EHRs would use this as a prior.

More low tech is that you and your physician are more vigilant when it comes to monitoring or testing for certain types of cancer if you have a high impact onco-variant.

Keep in mind that prognosis for cancer improves dramatically when you can detect it early.

[Gibbon1]

Even more sci-fi might be drugs that can mitigate the risk. Notable is the recent cocktail of drugs that coax the defective protein in CF to functioning better. There is one cancer gene I know that causes people to develop polyps in their intestines which then go on to become cancerous. Imagine a drug that stops that.

[pfisherman]

One of the weird things about oncogenes that I have observed is that there is a balance. Perturb them too far one way and you get cancer. Perturb them too far the other and you get a developmental disorder. This is not at all rigorously documented or studied. Just an anecdotal observation.