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

Although few studies have demonstrated utility of ¹⁸ F- fluoro-2-deoxy-d-glucose positron emission tomography/computerised tomography (¹⁸ F-FDG PET/CT) in benign pheochromocytoma/paragangliomas (PCC/PGLs), there limited data on factors predicting the FDG uptake in PCC/PGL.

The 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 ¹⁸ F-FDGPET/CT and majority (n = 78) underwent ¹³¹ I-metaiodobenzyl guanidine (¹³¹ I-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.

The 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 ¹³¹ I-MIBG and ¹⁸ F-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.

The study suggests that the underlying genetic status determines FDG uptake in PCC/PGL and not location, secretory status or malignancy.