SHH and esophageal squamous cell carcinoma: It has been well demonstrated that the activation of Shh signaling was involved in the development and progression of many types of cancer (Cui et al., 2010; Yoo et al., 2011; Wang et al., 2012; Duan et al., 2015), including ESCC (Berman et al., 2003; Yang et al., 2012).