CFTR and cystic fibrosis: However, as the CFTR biomarkers SCC, nPD and ICM also showed much lower heterogeneity in our previous studies on IVA monotherapy and combination therapies with LUM/IVA, TEZ/IVA and ELX/TEZ/IVA in CF patients older than 12 years, we conclude that CFTR biomarkers are more sensitive than the established clinical endpoints FEV1%predicted and BMI to detect partial functional rescue of mutant CFTR by CFTR modulator therapy (Graeber et al., 2015; Graeber et al., 2018; Graeber et al., 2022a).