PRNP and head and neck squamous cell carcinoma: As recently reported, PrPC is highly expressed in a variety of solid tumors, including gastric and colorectal cancer [25,26,27,28,29], breast cancer [30,31,32], prostate cancer [33], pancreatic ductal adenocarcinoma (PDAC) [34,35,36], lung adenocarcinoma [37], head and neck squamous cell carcinoma (HNSCC) [38], osteosarcoma [39], and melanoma [40,41].