SHH and pachyonychia congenita: Although the molecular causes of PC are largely elusive, studies have demonstrated that multiple critical genes, including K-Ras, p53, p16, and other key cellular signaling pathways such as PI3K/Akt, mammalian target of rapamycin (mTOR), nuclear factor-kappa B (NF-κB), epidermal growth factor receptor (EGFR), and sonic hedgehog (SHH) play important roles in the pancreatic tumorigenesis [26].