Chromogranin A in a Cohort of Pheochromocytomas and Paragangliomas: Usefulness at Diagnosis and as an Early Biomarker of Recurrence

Serum Succinate/Fumarate Ratio in Patients With Paraganglioma/Pheochromocytoma Attending an Endocrine Oncogenetic Unit

CONTEXT

Pheochromocytomas and paragangliomas (PPGLs) with SDHx pathogenic variants (PVs) are characterized by a higher intratissular succinate/fumarate ratio (RS/F) than non-SDHx-mutated ones. Also, an increase in serum succinate levels has been reported in patients with germline SDHB or SDHD PV.

OBJECTIVE

To assess whether measurement of serum succinate, fumarate levels, and RS/F might aid identification of an SDHx germline PV/likely pathogenic variant (LPV) in patients with PPGL or in asymptomatic relatives; and to guide identification of a PV/LPV among the variants of unknown significance (VUS) identified in SDHx by next-generation sequencing.

METHODS

This prospective monocentric study included 93 patients attending an endocrine oncogenetic unit for genetic testing. Succinate and fumarate were measured in serum by gas chromatography coupled to mass spectrometry. The RS/F was calculated to assess SDH enzymatic function. Diagnostic performance was assessed by receiver operating characteristic analysis.

RESULTS

RS/F had a higher discriminant power than succinate alone to identify an SDHx PV/LPV in patients with PPGL. However, SDHD PVs/LPVs are frequently missed. Only RS/F differed between asymptomatic SDHB/SDHD PV/LPV carriers and SDHB/SDHD-linked patients with PPGL. Finally RS/F could be helpful to easily evaluate the functional impact of VUS in SDHx.

CONCLUSION

Measurement of serum RS/F in patients with PPGL and in asymptomatic relatives is a valuable initial workup tool to detect those carrying a germline PV/LPV in SDHx. Its discriminative power is equal or superior to those of succinate measured alone. SDHD PVs/LPVs are less frequently identified by these biochemical tools. Use of RS/F for SDHx VUS reclassification needs to be evaluated further.

Biomarker response to high-specific-activity I-131 meta-iodobenzylguanidine in pheochromocytoma/paraganglioma

The objective of this study is to present the complete biomarker response dataset from a pivotal trial evaluating the efficacy and safety of high-specific-activity I-131 meta-iodobenzylguanidine in patients with advanced pheochromocytoma or paraganglioma. Biomarker status was assessed and post-treatment responses were analyzed for catecholamines, metanephrines, and serum chromogranin A. Complete biomarker response (normalization) or partial response, defined as at least 50% reduction from baseline if above the normal range, was evaluated at specified time points over a 12-month period. These results were correlated with two other study objectives: blood pressure control and objective tumor response as per RECIST 1.0. In this open-label, single-arm study, 68 patients received at least one therapeutic dose (~18.5 GBq (~500 mCi)) of high-specific-activity I-131 meta-iodobenzylguanidine. Of the patients, 79% and 72% had tumors associated with elevated total plasma free metanephrines and serum chromogranin A levels, respectively. Best overall biomarker responses (complete or partial response) for total plasma free metanephrines and chromogranin A were observed in 69% (37/54) and 80% (39/49) of patients, respectively. The best response for individual biomarkers was observed 6-12 months following the first administration of high-specific-activity I-131 meta-iodobenzylguanidine. Biochemical tumor marker response was significantly associated with both reduction in antihypertensive medication use (correlation coefficient 0.35; P = 0.006) as well as objective tumor response (correlation coefficient 0.36; P = 0.007). Treatment with high-specific-activity I-131 meta-iodobenzylguanidine resulted in long-lasting biomarker responses in patients with advanced pheochromocytoma or paraganglioma that correlated with blood pressure control and objective response rate. ClinicalTrials.gov number: NCT00874614.

Potential Biomarkers of Metastasizing Paragangliomas and Pheochromocytomas

Paragangliomas and pheochromocytomas (PPGLs) are rare neuroendocrine tumors originating from paraganglionic tissue in many sites of the body. Most PPGLs are characterized by nonaggressive behavior but all of them have the potential to metastasize. PPGLs represent a great diagnostic dilemma as it is difficult to recognize tumors that are likely to be metastasizing; criteria of malignancy can be found both in benign and metastatic forms. This review aims to analyze the current knowledge of the nature of metastasizing PPGLs paying particular attention to head and neck paragangliomas (HNPGLs). Potential predictors of the malignancy risk for PPGLs were summarized and discussed. These data may also help in the development of diagnostic and prognostic strategies, as well as in the identification of novel potential therapeutic targets for patients with PPGLs.

Pheochromocytomas and paragangliomas

PURPOSE OF REVIEW

Great progress has been made in understanding the genetic and molecular basis of pheochromocytoma and paragangliomas (PPGLs). This review highlights the new standards in the diagnosis and management of pediatric PPGLs.

RECENT FINDINGS

The vast majority of pediatric PPGLs have an associated germline mutation, making genetic studies imperative in the work up of these tumors. Somatostatin receptor-based imaging modalities such as 68Ga-DOTATATE and 64Cu-DOTATATE are shown to have the greatest sensitivity in pediatric PPGLs. Peptide receptor radionuclide therapies (PRRTs) such as 177Lu-DOTATATE are shown to have efficacy for treating PPGLs.

SUMMARY

Genetics play an important role in pediatric PPGLs. Advances in somatostatin receptor-based technology have led to use of 68Ga-DOTATATE and 64Cu-DOTATATE as preferred imaging modalities. While surgery remains the mainstay for management of PPGLs, PRRT is emerging as a treatment option for PPGLs.