CFTR and cystic fibrosis: The preliminary results of a complex phase II study investigating the safety and tolerability of VX-661 monotherapy and in combination with ivacaftor in patients who are homozygous for Phe508del and heterozygous for Phe508del/Gly551Asp CFTR mutations were presented at the 2014 North American Cystic Fibrosis Conference [75].