Genetic status determines 18 F-FDG uptake in pheochromocytoma/paraganglioma.

IntroductionAlthough few studies have demonstrated utility of F-18- fluoro-2-deoxy-d-glucose positron emission tomography/computerised tomography (F-18-FDG PET/CT) in benign pheochromocytoma/paragangliomas (PCC/PGLs), there limited data on factors predicting the FDG uptake in PCC/PGL. MethodsThe study was conducted at a tertiary health care centre. In addition to the routine investigations, all patients (n=96) with PCC/PGL were evaluated with F-18-FDGPET/CT and majority (n=78) underwent I-131-metaiodobenzyl guanidine (I-131-MIBG) scintigraphy. Forty-three patients also underwent testing for germline mutations in five PCC/PGL susceptibility genes (VHL, RET, SDHB, SDHC and SDHD) and all patients were evaluated clinically for neurofibromatosis-1. ResultsThe study included 96 patients with PCC/PGL(82 benign and 14 malignant). FDGSUVmax was significantly higher for malignant than benign PCC/PGL(P=0.009) and for extra-adrenal PGL than adrenal PCC (P=0.017). In subgroup analysis, metanephrine-secreting PCC and non-secretory PCC had significantly lower FDG SUVmax than normetanephrine-secreting PCC (P=0.017, P=0.038 respectively), normetanephrine-secreting-sympathetic PGL (P=0.008, P=0.019 respectively) and non-secretory sympathetic PGL (P=0.003, P=0.009 respectively). Patients with mutations in cluster 1 genes (n=14) had significantly higher FDG SUVmax than those with mutations in cluster 2 genes (n=4) (P=0.04). Sensitivities of I-131-MIBG and F-18-FDG PET/CTwere 77.78% and 100% for cluster 1 genes-related PCC/PGL whereas they were 100% and 50% for cluster 2 genes-related PCC/PGL, respectively. Multivariate regression analysis of mutation positive patients identified genetic status as the only independent predictor of FDG SUVmax. ConclusionThe study suggests that the underlying genetic status determines FDG uptake in PCC/PGL and not location, secretory status or malignancy.