RAC2 and head and neck squamous cell carcinoma: Proteins encoded by ARHGAP4 can regulate the binding between GTPase and rat sarcoma (RAS) family members, whose negative regulation involves the small G protein of the Rho family and associated with tumorigenesis in various cancers, including head and neck squamous cell carcinoma, glioblastoma, breast, lung, pancreatic, liver, colon, and prostate cancers (33, 34).