STK11 and Cowden disease: The most widely known HCSs include hereditary breast and ovarian cancer syndromes due to mutations in the BRCA1/2 genes [2, 3], Li–Fraumeni syndrome due to mutations in TP53 [4], Cowden syndrome due to mutations in PTEN [5], Lynch syndrome, in which mutations in the DNA mismatch repair system are involved [6, 7], diffuse gastric cancer syndrome caused by CDH1 gene mutation [8], Peutz–Jeghers syndrome caused by mutations in the STK11 [9] gene, and neurofibromatosis type 1 syndrome caused by NF1 mutations [10].