Many solid tumors, including pheochromocytoma (PHEO) and paraganglioma (PGL), are characterized by a (pseudo)hypoxic signature. (Pseudo)hypoxia has been shown to promote both tumor progression and resistance to therapy. The major mediators of the transcriptional hypoxic response are hypoxia-inducible factors (HIFs). High levels of HIFs lead to transcription of hypoxia-responsive genes, which are involved in tumorigenesis. PHEOs and PGLs are catecholamine-producing tumors arising from sympathetic- or parasympathetic-derived chromaffin tissue. In recent years, substantial progress has been made in understanding the metabolic disturbances present in PHEO and PGL, especially because of the identification of some disease-susceptibility genes. To date, fifteen PHEO and PGL susceptibility genes have been identified. Based on the main transcription signatures of the mutated genes, PHEOs and PGLs have been divided into two clusters, pseudohypoxic cluster 1 and cluster 2, rich in kinase receptor signaling and protein translation pathways. Although these two clusters seem to show distinct signaling pathways, recent data suggest that both clusters are interconnected by HIF signaling as the important driver in their tumorigenesis, and mutations in most PHEO and PGL susceptibility genes seem to affect HIF-α regulation and its downstream signaling pathways. HIF signaling appears to play an important role in the development and growth of PHEOs and PGLs, which could suggest new therapeutic approaches for the treatment of these tumors.

A B S T R A C T PurposeThe occurrence of Ն two distinct types of tumors, one of them paraganglioma (PGL), is unusual in an individual patient, except in hereditary cancer syndromes. Patients and MethodsFour unrelated patients were investigated, with thorough clinical evaluation. Plasma and tissue catecholamines and metanephrines were measured by high-performance liquid chromatography. Anatomic and functional imaging were performed for tumor visualization. Germline and tumor tissue DNA were analyzed for hypoxia-inducible factor 2 alpha (HIF2A) mutations. The prolyl hydroxylation and stability of the mutant HIF2␣ protein, transcriptional activity of mutant HIF2A, and expression of hypoxia-related genes were also investigated. Immunohistochemical staining for HIF1/2␣ was performed on formalin-fixed, paraffin-embedded tumor tissue. ResultsPatients were found to have polycythemia, multiple PGLs, and duodenal somatostatinomas by imaging or biochemistry with somatic gain-of-function HIF2A mutations. Each patient carried an identical unique mutation in both types of tumors but not in germline DNA. The HIF2A mutations in these patients were clustered adjacent to an oxygen-sensing proline residue, affecting HIF2␣ interaction with the prolyl hydroxylase domain 2-containing protein, decreasing the hydroxylation of HIF2␣, and reducing HIF2␣ affinity for the von Hippel-Lindau protein and its degradation. An increase in the half-life of HIF2␣ was associated with upregulation of the hypoxia-related genes EPO, VEGFA, GLUT1, and END1 in tumors. ConclusionOur findings indicate the existence of a new syndrome with multiple PGLs and somatostatinomas associated with polycythemia. This new syndrome results from somatic gain-of-function HIF2A mutations, which cause an upregulation of hypoxia-related genes, including EPO and genes important in cancer biology.