Background: Tezacaftor/ivacaftor is a CFTR modulator approved to treat people with cystic fibrosis (pwCF) who are homozygous (F/F) or heterozygous for the F508del-CFTR mutation and a residual function mutation (F/RF). This randomized, double-blind, placebo-controlled Phase 3 study evaluated the efficacy, safety, tolerability, and pharmacokinetics (PK) of tezacaftor/ivacaftor in participants ≥12 years of age heterozygous for the F508del-CFTR mutation and a minimal function mutation (F/MF), which produces no CFTR protein or a protein unresponsive to tezacaftor/ivacaftor in vitro., Methods: Participants were randomized 1:1 to receive tezacaftor/ivacaftor or placebo for 12 weeks. The primary endpoint was the absolute change from baseline in percent predicted forced expiratory volume in 1 second (ppFEV 1 ) between the tezacaftor/ivacaftor and placebo groups through week 12. Key secondary endpoints included absolute change from baseline in CF Questionnaire-Revised respiratory domain scores and the number of pulmonary exacerbations through week 12 and the absolute change from baseline in body mass index at week 12. A prespecified interim analysis (IA) for futility was conducted when approximately 50% of a planned enrollment of 300 participants reached week 12 of the study., Results: At the time of the IA, 83 participants were randomized to tezacaftor/ivacaftor and 85 to placebo; 165 participants completed treatment. The study failed to demonstrate that tezacaftor/ivacaftor significantly improved ppFEV 1 or any of the key secondary endpoints and was terminated for futility. The safety profile and PK parameters of tezacaftor/ivacaftor were similar to those reported in prior studies in participants ≥12 years of age with CF., Conclusions: Tezacaftor/ivacaftor did not show a clinically meaningful benefit in participants with F/MF genotypes but was generally safe and well tolerated, consistent with the safety profile reported in other Phase 3 studies (NCT02516410)., Competing Interests: Declaration of Competing Interest All authors received nonfinancial support (assistance with manuscript preparation) from ArticulateScience LLC, which received funding from Vertex Pharmaceuticals Incorporated. Additional disclosures are as follows: DC, CAO, NA, and LTW are employees of Vertex Pharmaceuticals Incorporated and may own stock or stock options in Vertex Pharmaceuticals Incorporated. AM: Coordinator for the Vertex tezacaftor/ivacaftor clinical trial 661-107 and fees for their institution (Robert Debré Hospital, Paris, France) during the conduct of the study; participation in advisory boards and educational meetings with Vertex Pharmaceuticals Incorporated outside of the submitted work. CW: Income on a per-patient basis derived from pharmaceutical studies (Vertex Pharmaceuticals Incorporated and Boehringer-Ingelheim); research grant from Novo Nordisk Pharmaceuticals for the P/L-CF-IDEA study; Vertex Pharmaceuticals P/L honorarium to attend the CF International Advisory Board Meeting in February 2014; Vertex Pharmaceuticals P/L honorarium to attend CF Medical Advisory Board Meeting in Adelaide in April 2014; Novartis Pharmaceuticals P/L honorarium to present a symposium at the National Pediatric Congress in Lebanon in May 2014; Vertex Pharmaceuticals P/L return travel and honorarium for lecture & discussions at the European CF Conference in Gothenburg in June 2014; DKBmed, LLC honorarium to present symposium at the North American CF Conference Georgia in October 2014; Vertex Pharmaceuticals P/L honorarium to present as speaker in an educational meeting series in Brisbane and Sydney in April 2015; Vertex Pharmaceuticals P/L honorarium to attend the Vertex Steering Committee Meetings on the VX15-770-123 study in 2014; Vertex Pharmaceuticals P/L honorarium for Vertex Medical Advisory Board-Innovative endpoints in CF in August 2015; University of Miami honorarium for meeting attendance in 2015; Thorax honorarium for associate editor duties in Q3/Q4 2015; BMJ honorarium for work as a reviewer; Vertex Pharmaceuticals 2015 Chicago return flight and accommodation for work as investigator in lumacaftor study; Vertex Pharmaceuticals 2015–2017 honorarium for being a speaker at Vertex-sponsored educational meeting series in Australia; Vertex Pharmaceuticals 2016 Phoenix return flight and accommodation as investigator in the Next Gen study; Vertex Pharmaceuticals December 2016 honoraria for work as a speaker at a Vertex-sponsored educational meeting in Liverpool, UK; DKBmed eCF review issue honoraria in January 2017; Vertex Pharmaceuticals March 2017 honoraria for being a speaker at TSANZ meeting; Vertex Pharmaceuticals Incorporated 2014–2018 honorarium for acting as a consultant on the Vertex Orkambi 6-11 HTA Advisory Board, the Global Pediatric Advisory Committee, the Global Medical Advisory Board, and the VIA Grants Committee; Gilead Sciences Ltd. honorarium for meeting attendance on CF imaging; honorarium for In Vivo Academy Limited for webcast meeting attendance at ECFC 2018; Vertex Pharmaceuticals P/L honorarium to present as a speaker in an educational meeting at ECFC in Belgrade 2018; Vertex Pharmaceuticals Incorporated honorarium to attend the Next Gen Early Lifecycle Management Plan in London in 2018; Vertex Pharmaceuticals P/L to act as consultant and to render such services in the form of documents, advice, meetings, and conferences from October 2018 to present; Vertex Pharmaceuticals (Australia) P/L to attend as a steering committee member at the Medical Symposium Event (SHIFT 2019) in Perth in 2019; Vertex Pharmaceuticals P/L to attend the EU Real World Evidence steering committee in Amsterdam in 2019; Current board positions: International Advisory Board, Vertex Pharmaceuticals P/L; Associate Editor, Thorax; Associate Editor, Respirology. EK: Grants from Vertex Pharmaceuticals Incorporated during the conduct of the study; speaker honorarium and membership in scientific advisory board at Vertex Pharmaceuticals Incorporated outside the submitted work. HE: participated in an advisory board meeting with Vertex Pharmaceuticals Incorporated outside of the submitted work., (Copyright © 2020 The Author(s). Published by Elsevier B.V. All rights reserved.)