RET and pheochromocytoma: PGLs or pheochromocytomas that are linked to a pseudohypoxic pathway (e.g., SDHx, VHL, HIF2a, FH, MDH2, PHD1/EGLN2, PHD2/EGLN1) are referred to as Cluster 1 disease, whereas tumors that are linked to a cluster rich in kinase receptor signaling pathways (e.g., RET, TMEM127, MAX, NF1, KIF1Bβ) are referred to as Cluster 2 disease.