According to the article, 10 to 15% of all colon cancers are caused by the gene. To keep things simple, say
Pr(they have the gene | person has colon cancer) = .12
Pr(person has the gene) =1/200
For those people with the gene the risk of getting colon cancer is 70-90%. Estimate:
Pr (getting cancer | person has the gene) = .8
So one can ask for Pr((getting colon cancer|does not have the gene) (this seems to require a bit of algebra).. Also one can derive Pr(getting colon cancer).