Peter van Mourik

153 Personalized treatment of CF using rectal organoids CONCLUSION In vitro drug efficacy measurements by FIS in rectal organoids of individuals with CF correlate with the most important in vivo response indicators of CFTR modulators (change in ppFEV 1 and SCC). The data further suggest that thresholds can be established to prospectively identify clinical responders with acceptable positive and negative predictive values. Organoid testing can provide a patient-friendly and cost- effective approach to increase access to treatment for patients with CF, and optimize risk-benefit and cost-effectiveness of treatments. This study is a first example that in vitro tests using cultures of patient stem cells, stored in a living biobanks, can be used to predict individual treatment benefits. 7