A phase I trial of ivosidenib in 21 IDH-mutated CS patients (ClinicalTrials.gov ID: NCT04278781) resulted in a median progression-free survival (PFS) of 5.6 months, where the best overall response was stable disease in 52% of the patients, and no complete responses or partial responses were observed during the first two years [90]. Here, IDH1 is linked to Cowden syndrome 1.