Introduction: 18F-FDOPA illustrates the properties of uptake and storage of catecholamines in pheochromocytomas (PHEOs). Until now, the relationship between 18F-FDOPA quantitative parameters and a PHEO secretory profile has not been specifically evaluated.
Materials and methods: Fifty-six patients (56% females, median age: 47.5 yrs) with non-metastatic PHEO, evaluated by 18F-FDOPA PET/CT, were included in this retrospective study. Forty-five patients had negative genetic testing (80.4%); five patients (8.9%) had RET, two patients (3.6%) had SDHB, two had SDHD (3.6%), one patient (1.8%) had NF1, and one patient had a VHL (1.8%) mutation. Correlation between 18F-FDOPA metabolic parameters (tumor SUVmax, tumor SUVmean, tumor SUVmax/liver SUVmax, MTV 42%, total lesion uptake), urinary metanephrines (MNs), and plasma chromogranin A (CgA) were evaluated.
Results: All patients had positive 18F-FDOPA PET/CT. On univariate analysis, there was a strong correlation between all metabolic parameters and urinary MNs and plasma chromogranin A (CgA). The highest correlations were observed between total lesion (TL) uptake and the value of urinary MNs regardless of their nature (p = 8.10-15 and r = 0.80) and between MTV 42% and plasma CgA levels (p = 2.10-9, r = 0.74). On multivariate analysis, the correlation of uptake parameters and CgA levels did not persist further due to the relation of CgA and tumor diameter. A correlation between TL uptake and the normetanephrine/metanephrine ratio (NMN/MN) was also found, a finding that was in accordance with in vitro studies, which were found to have a higher catecholamine content in epinephrine producing PHEOs.
Conclusion: This retrospective study shows a correlation between 18F-FDOPA uptake, especially using TL uptake, urinary MNs, and a PHEO biochemical phenotype. This illustrates that beyond its localization value, 18F-FDOPA PET further enables PHEO characterization at a specific metabolic level.
Keywords: Pheochromocytomas · 18F-FDOPA · Radionuclide imaging · Genetics.