SHH and cancer: Our previous findings of the invariable loss of Shh in murine and human urothelial carcinomas (Shin et al., 2014b), together with studies of other solid tumors, strongly support a role of Shh as a tumor suppressor during cancer progression (Lee et al., 2014; Rhim et al., 2014; Yang et al., 2017), raising the important questions concerning the molecular mechanisms by which the expression of Shh is lost in tumor cells at early stages of carcinoma development.