Pheochromocytoma: Gasping for Air.

There has been increasing evidence that pseudohypoxia--a phenomenon that we refer to as "gasping for air"--along with mitochondrial enzyme dysregulation play a crucial role in tumorigenesis, particularly in several hereditary pheochromocytomas (PHEOs) and paragangliomas (PGLs). Alterations in key tricarboxylic acids (TCA) cycle enzymes (SDH, FH, MDH2) have been shown to induce pseudohypoxia via activation of the hypoxia-inducible transcription factor (HIF) signaling pathway that is involved in tumorigenesis, invasiveness, and metastatic spread, including an association with resistance to various cancer therapies and worse prognosis. This review outlines the ongoing story of the pathogenesis of hereditary PHEOs/PGLs, showing the unique and most updated evidence of TCA cycle dysregulation that is tightly linked to hypoxia signaling.