SHH and melanoma: Upregulation of EGFR and platelet-derived growth factor receptor (PDGFRβ) by TGF-β signaling leads to resistance to BRAF and MEK inhibitors (36), and upregulation of PDGFRα by the Sonic Hedgehog Homolog (Shh) pathway confers resistance to BRAF inhibition in metastatic BRAF(V600E) melanoma (37).