Phaeochromocytomas and paragangliomas (PPGLs) are highly heterogeneous tumours that based on gene expression profiling fall into two cluster groups: cluster 1 PPGLs are phenotypically immature tumours due to mutations resulting in activation of hypoxia-angiogenic pathways; cluster 2 tumors are more mature adrenaline-producing tumours caused by mutations of genes leading to activation of kinase signalling pathways. Among cluster 1 tumours, those due to mutations in genes encoding succinate dehydrogenase (SDH) subunits and other Krebs cycle energy pathway enzymes are more often malignant than other PPGLs. Tumourigenic mechanisms responsible for SDH-mutated PPGLs involve a block in Krebs cycle energy pathway conversion of succinate to fumarate with resulting highly elevated tumour tissue levels of succinate. The extent of increase in succinate relative to the decrease in fumarate, reflecting the degree of functional impairment of SDH, varies depending on the SDH subunit affected. PPGLs due to SDHB mutations are more prone to malignancy and also exhibit more pronounced impairment of SDH function than PPGLs due to other SDH mutations. Succinate acts as an oncometabolite that inhibits alpha-ketoglutarate-dependent enzymes, including prolyl hydroxlases responsible for proteosomal degradation of hypoxia inducible factors, including the HIF2α expressed in cluster 1 PPGLs. For SDHB-mutated tumours, additional succinate mediated inhibition of DNA methyltransferases also leads to a hypermethylator phenotype and further silencing of genes involved in controlling proliferation. The inverse relationship between differentiation and disease aggressiveness reflects chanelling of energy to tumour growth in SDHB-mutated PPGLs. These considerations point to possible therapeutic targets. The block in oxidative phosphorylation at complex II implies a need for alternative energy sources for tumour growth and a possible Achilles’ heel for targeted therapies for metastatic PPGLs. Reversing the DNA hypermethylation in SDHB-mutated metastatic PPGLs provides another potential therapeutic strategy. A third strategy involves blockade of HIF2α or its downstream signalling pathways.