Purpose: The occurrence of ≥ two distinct types of tumors, one of them paraganglioma (PGL), is unusual in an individual patient, except in hereditary cancer syndromes.
Patients and methods: Four 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 HIF2α protein, transcriptional activity of mutant HIF2A, and expression of hypoxia-related genes were also investigated. Immunohistochemical staining for HIF1/2α was performed on formalin-fixed, paraffin-embedded tumor tissue.
Results: Patients 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 HIF2α interaction with the prolyl hydroxylase domain 2-containing protein, decreasing the hydroxylation of HIF2α, and reducing HIF2α affinity for the von Hippel-Lindau protein and its degradation. An increase in the half-life of HIF2α was associated with upregulation of the hypoxia-related genes EPO, VEGFA, GLUT1, and END1 in tumors.
Conclusion: Our 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.