PTCH2 and breast cancer: A new molecular target in the potential treatment of tamoxifen-resistant breast cancer is the Hedgehog signalling pathway, along with the proteins patched 1 and patched 2 (PTCH1 and PTCH2), Hedgehog-interacting protein HHIP and Glioma-associated oncogene homolog 1 and 2 (GLI1/GLI2), which can trigger positive or negative feedback in this pathway [236].