CFTR and cystic fibrosis: Background: Elexacaftor/tezacaftor/ivacaftor (ETI) is the newest cystic fibrosis transmembrane conductance regulator (CFTR) modulator drug approved for the treatment of patients with cystic fibrosis (pwCF) aged ≥6 years with at least one copy of the F508del mutation (F) in the CFTR gene or another mutation that is responsive to treatment with ETI.