A good test is clinically useful
As gene tests are applied to more genes and people, they are detecting rarer gene variants, those that confer smaller additional risks, and an increasing number of gene variants of unknown significance (VUS). Amid the growing challenges of grading ever more variation in normal human genomes and in genes that contribute to cancer, researchers are using many different strategies to improve the positive predictive value (PPV) of the tests. PPV is the most important measure of clinical utility of a test \cite{Burke_2014}, being the probability that a positive test identifies a variant that actually results in a cancer in that person. Tests can also be clinically useful if they have a high negative predictive value (NPV) being the probability that a negative test results in no cancer in that person. Consequently, the more we know about the gene, genome, heritable cancer predisposition and the person tested, the higher the predictive values and the greater the clinical utility of these tests.