First, there is evidence that in Ptch1−/− cells, such as ASZ001 cells, Ptch2 mediates the Shh response [50], that like Ptch1, Ptch2 exerts a tumor-suppressive function in basal cell carcinoma cells, and that only after targeting of both paralogs becomes the activation of the hedgehog pathway independent of hedgehog ligand [51]. The gene discussed is PTCH1; the disease is basal cell carcinoma.