New syndrome of paraganglioma and somatostatinoma associated with polycythemia

Abstract

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.

Fig 1.

Functional and anatomic imaging. (A) ¹⁸F-fluorodopa positron emission tomography (PET)/computed tomography (CT) in patient 2 showing (a) small focus at base of skull consistent with glomus jugulare tumor, (b) focus at medial edge of liver, (c) aortocaval node at L1/L2 vertebral disc level, (d) another aortocaval focus at L2/L3 vertebral disc level, (e) left periaortic focus at L4/L5 disc level, and (f) right presacral focus in upper pelvis. (B) ¹⁸F-fluorodopamine PET/CT in patient 2 also showed (a) focus at base of skull, (b) focus at medial edge of liver or in adjacent node, (c) aortocaval node at L1/L2 disc level, (d) another aortocaval focus at L2/L3 vertebral disc level, (e) left periaortic focus at L3/L4 disc level (not seen on ¹⁸F-fluorodopa PET/CT), (f) probable common iliac node at L4/5 disc level, and (g) presacral focus on right in upper pelvis. (C, D) Early arterial phase of axial CT of abdomen performed with negative enteric contrast in patient 3 showed (a) mass protruding into lumen in distal second portion of duodenum, near junction with third portion, (b) paraduodenal/parapancreatic node, and (c) another small mass in second portion of duodenum.

Fig 2.

Tumor tissue immunostaining for hypoxia-inducible factor 2 alpha (HIF2α) expression and EPO mRNA expression in tumor tissue obtained from patients. (A) Immunohistochemical staining for HIFs in tumor sections (top row, paraganglioma [PGL]; bottom row, somatostinoma) obtained from patient 1, showing nuclear staining (black arrows) for HIF2α (right column) in contrast to HIF1α (left column; scale, 100 mm; magnification, 80×). (B) Comparison of EPO mRNA expression assessed by quantitative polymerase chain reaction in PGLs (indicated by P) obtained from patients 1 and 4 and in somatostatinoma obtained from patient 1 (indicated by S) with expression in PGLs from patients with germline SDHB, SDHD, MAX, and RET mutations, patients with multiple endocrine neoplasia type 1 (MEN1), and patients with normal adrenal medulla (NAM). Bars indicate SE.

Fig 3.

Summary of pathways affecting hypoxia-inducible factor (HIF) turnover involved in development of various paragangliomas (PGLs), some associated with either somatostatinoma or polycythemia. (1) Somatic gain-of-function HIF2A mutations have been described in this report to be associated with multiple PGLs, somatostatinoma, and polycythemia. These mutations affect prolyl hydroxylation and pVHL (Von Hippel–Lindau protein) protein binding and reduce HIF2α degradation but not transcriptional activity. pVHL is part of an E3 ubiquitin ligase complex that targets HIFα for proteasomal degradation. Interaction of pVHL with HIFα is determined by hydroxylation status of HIFα proline residues. This hydroxylation is oxygen (O₂) dependent and catalyzed by family of prolyl hydroxylases (PHD1-3). HIFα stabilization can occur as a result of mutations in either PHD or VHL. (2) Germline mutations in PHD2 have been associated with congenital polycythemia and extra-adrenal PGLs. (3) VHL mutations prevent pVHL from binding hydroxylated HIFα and targeting it for proteasomal degradation. As a result of either PHD or VHL mutation, HIFα accumulates in cytoplasm, translocates to nucleus, forms heterodimers with HIFβ, and activates transcription of target genes. In pVHL-defective PGLs, there is evidence of increased HIF activity. CBP, cAMP-response element-binding protein; CO₂, carbon dioxide; cul2, cullin 2; EMT, epithelial-mesenchymal transition; EPO, erythropoietin; ODD, oxygen-dependent degradation; OH, hydroxyl group; p300, histone acetyltransferase p300; Rbx1, ring-box 1 protein; Ub, ubiquitin.