Clinical, Diagnostic, and Treatment Characteristics of SDHA -Related Metastatic Pheochromocytoma and Paraganglioma.

Background: Pheochromocytoma and paraganglioma (PHEO/PGL) are rare neuroendocrine tumors which may cause potentially life-threatening complications, with about a third of cases found to harbor specific gene mutations. Thus, early diagnosis, treatment, and meticulous monitoring are of utmost importance. Because of low incidence of succinate dehydrogenase complex subunit A ( SDHA )-related metastatic PHEO/PGL, currently there exists insufficient clinical information, especially with regards to its diagnostic and treatment characteristics. Methods: Ten patients with SDHA -related metastatic PHEO/PGL were followed-up prospectively and/or retrospectively between January 2010-July 2018. They underwent biochemical tests ( n = 10), 123 I-MIBG ( n = 9) scintigraphy, and multiple whole-body positron emission tomography/computed tomography (PET/CT) scans with 68 Ga-DOTATATE ( n = 10), 18 F-FDG ( n = 10), and 18 F-FDOPA ( n = 6). Results: Our findings suggest that these tumors can occur early and at extra-adrenal locations, behave aggressively, and have a tendency to develop metastatic disease within a short period of time. None of our patients had a family history of PHEO/PGL, making them appear sporadic. Nine out of 10 patients showed abnormal PHEO/PGL-specific biochemical markers with predominantly noradrenergic and/or dopaminergic phenotype, suggesting their utility in diagnosing and monitoring the disease. Per patient detection rates of 68 Ga-DOTATATE ( n = 10/10), 18 F-FDG ( n = 10/10), 18 F-FDOPA ( n = 5/6) PET/CT, and 123 I-MIBG ( n = 7/9) scintigraphy were 100, 100, 83.33, and 77.77%, respectively. Five out of 7 123 I-MIBG positive patients had minimal 123 I-MIBG avidity or detected very few lesions compared to widespread metastatic disease on 18 F-FDG PET/CT, implying that diagnosis and treatment with 123/131 I-MIBG is not a good option. 68 Ga-DOTATATE PET/CT was found to be superior or equal to 18 F-FDG PET/CT in 7 out of 10 patients and hence, is recommended for evaluation and follow-up of these patients. All 7 out of 7 patients who received conventional therapies (chemotherapy, somatostatin analog therapy, radiation therapy, 131 I-MIBG, peptide receptor radionuclide therapy) in addition to surgery showed disease progression. Conclusion: In our cohort of patients, SDHA -related metastatic PHEO/PGL followed a disease-course similar to that of SDHB -related metastatic PHEO/PGL, showing highly aggressive behavior, similar imaging and biochemical phenotypes, and suboptimal response to conventional therapies. Therefore, we recommend careful surveillance of the affected patients and a search for effective therapies.