Second, mutations in SMO or in other HH pathway targets (upstream such as Protein patched homolog 1 (PTCH1), or downstream such as glioma-associated oncogenes 1/2 (GLI1/2) or v-myc myelocytomatosis viral-related oncogene (MYCN)) have been discovered to drive BCC progression and are also involved in acquired treatment resistance against HHI [17,18,19]. This evidence concerns the gene PTCH1 and skin basal cell carcinoma.