Known knowns
Identifying the known knowns is getting more complex. Panels of known high penetrance cancer-causing genes are scrutinized by DNA sequencing in individuals who qualify because of clinical and family history. For each type of cancer there are different criteria, for instance for high risk of hereditary breast-or-ovarian cancer or hereditary non-polyposis colon cancer respectively. However, the set of cancers caused by each mutated gene is broader than initially appreciated \cite{LaDuca_2019}, so it may be necessary to broaden the set of clinical features used to justify testing, extend the set of genes on the test panel, or include more individuals in familial testing. Still, it is worth bearing in mind that prediction of the site of any future cancer, or the outcome of an existing tumor becomes more difficult as the complexity of the genetic test and its applications grow.