Based on the main signaling pathway signatures resulting from hereditary and sporadic pheochromocytoma gene mutations, pheochromocytomas are divided in two main gene expression clusters (17–19): The first group, pseudo-hypoxia cluster, included tumors carrying SDHx (cluster 1A) and VHL (cluster 1B) mutations, which accounts for 30% of the sporadic tumors. This evidence concerns the gene VHL and hereditary pheochromocytoma-paraganglioma.