Background: The expression of vesicular catecholamine transporters (VMAT1 and 2) in pheochromocytomas (PHEOs) and paragangliomas (PGLs) and the possible relationships with [18F]FDOPA PET/CT and [123I]MIBG scintigraphy uptake are unknown. Our purpose was to investigate possible correlations of either VMAT1 and VMAT2 expression with the functional imaging in patients with PHEOs and PGLs.
Methods: An observational 3-year time study was performed by enrolling 31 consecutive patients with PHEO (N.=17) or PGL (N.=14). They underwent the same diagnostic work-up; moreover, [123I]MIBG SPECT/CT (N.=20) and [18F]FDOPA PET/CT (N.=14) were performed in a subset of patients. After surgery, routine histology and semiquantitative analysis of VMAT1/VMAT2 immunoreactivity were carried out in all cases.
Results: VMAT1 immunoreactivity was found in all tumors, but two PHEOs. VMAT1 immunoreactivity was higher in PGLs than in PHEOs, though at not significant extent. Elevated VMAT2 immunoreactivity score was present in all but two negative tumors. Normal [123I]-MIBG uptake was independent from VMAT1/2 immunoreactivity. Patients undergoing [18F]FDOPA PET/CT showed a high score level of both VMATs and were detected by the technique in all cases.
Conclusions: VMAT1 and VMAT2 are highly expressed in most tumors, though VMAT1 immunoreactivity is apparently prevalent in PGLs as compared to PHEOs. Presence and expression of VMAT1 and VMAT2 are not limiting factors for MIBG uptake. The status of VMAT expression might help to understand why the more frequently used radiotracers do not always have the expected diagnostic performance. Finally, the present study points out the importance of developing new radiotracers with higher sensitivity, specificity and accuracy consequently reducing healthcare costs.