Similar clinical utility and wide‐spread adoption have been demonstrated for a rapidly growing list of “companion diagnostic” tests to identify specific tumor variations that predict drug‐specific anti‐cancer efficacy, as well as testing for mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene that inform drug selection and efficacy in the treatment of CF.5, 6. The gene discussed is CFTR; the disease is cystic fibrosis.