Germline mutations of PTEN are the cause of four autosomal dominant inherited syndromes: Cowden syndrome (CS) [21], Bannayan–Riley–Ruvalcaba syndrome (BRRS) [22,23], Proteus syndrome (PS), and PS-like syndrome [24], which share common features, including the development of multiple benign hamartomas, and are all classified under the umbrella term of the PTEN hamartoma tumour syndromes (PTHSs) [12,13]. This evidence concerns the gene PTEN and Cowden syndrome 1.