RAP1B and esophageal squamous cell carcinoma: The expression level of RAS-associated protein 1b (Rap1b), as a member of the RAS superfamily, has been confirmed to correlate positively with stemness of CSCs, and overexpression of Rap1b in ESCC positively regulates CSC proliferation, invasion, and stemness, making it a novel target for reversing ESCC drug resistance (Noguchi et al., 2015; Jia et al., 2017; Zhang et al., 2019).