ACE2 is downregulated in hepatocellular carcinoma (59), non-small cell lung cancer (NSCLC) (60), breast tumors (61), pancreatic ductal adenocarcinoma (62), and gallbladder cancer (63); ACE2 and TMPRSS2 are both upregulated in colorectal tumor (64) and lung cancer (65). TMPRSS2 is downregulated in head and neck cancer (66). Here, ACE2 is linked to head and neck cancer.