Personalized diagnostics of chromaffin tumors (pheochromocytoma, paraganglioma) in oncoendocrinology

Abstract

Pheochromocytomas and paragangliomas (PPGLs) are rare catecholamine-secreting neuroendocrine tumours, up to 40% of which occur in the setting of a hereditary syndrome. The incidence is 2 to 8 per million persons per year. The peak incidence occurs in the third to fifth decades of life. According to the most recent classification, chromaffin tumours refer to malignant neoplasms. The incidence of metastasis in pheochromocytomas is 10%; in paragangliomas it is 25%. Clinical manifestations of PPGLs are caused by the excess of catecholamines. More than 20 hereditary gene mutations are known to result in PPGLs development. According to the molecular and cellular pathophysiology, all currently known mutations can be divided into 2 groups: the first group – SDHх, SDHAF2 (the assembly factor of SDH, FH, MDH2) – disrupts the Krebs cycle and mitochondrial energy transport chain; the second group – RET, NF1, TMEM127, MAX – leads to mutations in receptor protein kinases (tyrosine kinase), activating intracellular signal pathways (PI3K-AKT-mTOR and MYC), which are responsible for cell growth, growth regulation and cell differentiation. As a result, HIF transcription factors are stabilized (oxidative stress), and DNA methylation is changed, which leads to severe disturbances in gene expression and to malignant transformations of cells. There are three main biochemical phenotypes of PPGLs: noradrenergic, adrenergic and dopaminergic. According to the tumor type, the patient’s age and family history, complementary genetic testing and molecular visualization are recommended. In clinical practice, the biochemical tumor phenotype, its stage, family history and especially the genetic tumor “passport” allow to choose the best molecular visualization method (SPECT-CT/PET-CT) to personalize treatment and prognosis.