The stromal compartment responds to Hedgehog ligands secreted by tumor cells to support the latter indirectly, in contrast to other Hedgehog driven cancers, such as basal cell carcinoma, where the Hedgehog pathway is often upregulated through loss of function mutations in Patched homologue 1 (PTCH1) [122,123]. Here, PTCH1 is linked to neoplasm.