SMO and skin basal cell carcinoma: Additionally, mutations that result in overproduction of Hh ligands in breast cancer [41] and BCC [42], loss of PTCH receptor function in BCC [43] and gastric cancer [44], as well as upregulation of SMO activity in pancreatic cancer stroma [45] and BCC [46] can lead to constitutively activated Hh signaling [47].