Furthermore, as central CS may occur in a small proportion of patients with fibrous dysplasia, a benign fibro‐osseous tumour caused by pathognomonic GNAS hotspot mutations [24], we assessed if detection of mutant GNAS molecules in plasma could also be employed in a similar manner to that of IDH1/2‐mutated ctDNA. This evidence concerns the gene GNAS and Cowden syndrome 1.