PGL4 is characterized by pheochromocytoma and paraganglioma, type 2 (SDHB negative) gastrointestinal stromal tumors and renal tumors, which are usually classified as carcinoma.
False-negative ¹²³I-MIBG SPECT is most commonly found in SDHB-related pheochromocytoma or paraganglioma with high frequency to develop metastatic disease.
We have identified the first pathway that distinguishes SDHB-metastatic from all other types of pheochromocytomas/paragangliomas and suggest that activation of the EMT process might play a critical role in the particularly invasive phenotype of this group of tumors.
In conclusion, in our multicentric database of PC-PGLs from Belgium, (i) the prevalence of SDHx mutations was high in hnPGLs (44% in the whole subset, 37% of apparently sporadic cases); (ii) in sporadic cases, the prevalence of SDHB mutations was high (20%), similar to that of SDHD (18%); and (iii) no SDHx mutation was found in a subset of mostly adrenal, benign PCs.
It is now recognized that all of the SDH genes are involved in the tumorigenesis of not only paragangliomas/pheochromocytomas, but also other tumor types, most notably gastrointestinal stromal tumors.
Although a variety of missense mutations in the coding sequence of the SDHB gene have been found in PHEOs and PGLs, it has been unclear whether these mutations impair mRNA expression, protein stability, subcellular localization, or intrinsic protein function.
(18)F-DOPA PET is a sensitive and specific imaging modality for the detection and staging of pheochromocytomas and paragangliomas in different genotypes, including VHL-, SDHB-, and SDHD-mutation carriers, and in patients with no germline mutation.
SDHA and SDHB immunohistochemistry are reliable techniques to identify pheochromocytomas and paragangliomas with mutations in SDHA, SDHB, SDHC and SDHD.
Using the yeast model, here, we report functional investigations on several missense SDH mutations found in patients affected by pheochromocytomas or paragangliomas.
Genetic analysis for PHEO/paraganglioma genes (SDH A-D, SDHAF2, RET, VHL, TMEM127, and MAX), and pituitary-related genes (AIP, MEN1, and p27) were negative.
The dysfunction of genes involved in the cellular response to hypoxia, such as VHL, EGL nine homolog 1, and the succinate dehydrogenase (SDH) genes, leads to a direct abrogation of hypoxia inducible factor (HIF) degradation, resulting in a pseudo-hypoxic state implicated in PCC/PGL development.
PCC/PGL are still thought of as the "tumor of tens," with 10 % being hereditary; however, recent population based studies suggest that up to 32 % of patients have a germline mutation in one of the known common susceptibility genes (including NF1, VHL, RET, SDHB, SDHD, and SDHC).
Unsupervised analysis identified two dominant clusters, separating SDHB and SDHD-AT PHEOs/PGLs (cluster A) from VHL PHEOs and SDHD-HN PGLs (cluster B).
Finally, global proteomic analysis in SDHB and MAX tumors allowed us to determine that miRNA regulation occurs primarily through mRNA degradation in PCCs/PGLs, which partially confirmed our miRNA-mRNA integration results.
Patients with germline mutations in one of the SDH genes are at substantially increased risk of developing paragangliomas, pheochromocytomas (pheos), and other tumors (all combined referred to as SDH-related tumors).
Paraganglioma/pheochromocytoma syndrome (PGL/PCC syndrome) consists of different entities, associated with germline mutations in five different genes: SDHD, SDHAF2, SDHC, SDHA and SDHB.
Important new findings are that mutations of succinate dehydrogenase genes SDHA, SDHB, SDHC, SDHD, and SDHAF2 (collectively "SDHx") are responsible for a large percentage of hereditary PCC/PGL and that SDHB mutations are strongly correlated with extra-adrenal tumor location, metastasis, and poor prognosis.
However, while SDHB protein expression as determined by IHC in a small cohort of tumors was lower in PCCs than in the surrounding adrenal cortex, there was no obvious correlation with LOH or the level of SDHAF2/SDHD mRNA expression.
About 60% of Pheochromocytoma (PCC) and Paraganglioma (PGL) patients have either germline or somatic mutations in one of the 12 proposed disease causing genes; SDHA, SDHB, SDHC, SDHD, SDHAF2, VHL, EPAS1, RET, NF1, TMEM127, MAX and H-RAS.
We hypothesised that PC/PGLs containing SDHx or VHL mutations, and succinate dehydrogenase (SDH)-deficient gastrointestinal stromal tumours (GISTs), would overexpress miR-210 relative to non-SDH or -VHL-mutated counterparts. miR-210 was analysed by quantitative PCR in i) 39 PC/PGLs, according to genotype (one SDHA, five SDHB, seven VHL, three NF1, seven RET, 15 sporadic, one unknown) and pathology (18 benign, eight atypical, 11 malignant, two unknown); ii) 18 GISTs, according to SDHB immunoreactivity (nine SDH-deficient and nine SDH-proficient) and iii) two novel SDHB-mutant neurosphere cell lines. miR-210 was higher in SDHx- or VHL-mutated PC/PGLs (7.6-fold) compared with tumours without SDHx or VHL mutations (P=0.0016). miR-210 was higher in malignant than in unequivocally benign PC/PGLs (P=0.05), but significance was lost when benign and atypical tumours were combined (P=0.08).