Endocrine Abstracts

Phaeochromocytomas (PHAEOs) and extra-adrenal paragangliomas (PGLs) are rare neuroendocrine tumours. As many as 35% may have an identifiable germline mutation, most commonly in the genes encoding RET, VHL or subunits of succinate dehydrogenase (SDHx).

[¹²³I]-labelled metaiodobenzylguanidine (¹²³I-MIBG) scintigraphy is used to localise PHAEOs/PGLs, while ¹³¹I-MIBG is used as therapy in malignant disease. Uptake of radioisotope may vary with genotype; ¹⁸F-FDG–PET is more sensitive than MIBG in tumours associated with SDHB mutations. We compared MIBG avidity in genetically defined PHAEO/PGL patients with those without mutations in RET, VHL or SDHx.

We undertook a clinical record review of 55 patients with histologically proven PHAEOs/PGLs attending the Endocrinology Unit at the Western Infirmary, Glasgow.

Forty three of the 55 had genetic testing performed; in 31/43 (72%) a genetic mutation was identified. 18 (41.9%) had an SDHB mutation and 4 (9.3%) had an SDHD mutation; 6 (13.9%) had a mutation in VHL; 3 (7.0%) had a mutation in RET, and 12 (27.9%) had negative genetic testing.

Pre-operative MIBG scans were performed in 39 of 55 patients. 33 patients (84.6%) had MIBG avid tumours. 11/13 (84.6%) patients with an SDHB mutation were MIBG avid; 1/2 (50%) SDHD mutations were MIBG avid (total SDHx mutation group 12/15 (80%) MIBG avid). The other populations were as follows: RET 2/2 (100%); VHL 3/3 (100%); and sporadic 7/8 (87.5%) MIBG avid.

We found a higher than anticipated proportion of PHAEOs/PGLs with an identifiable germline mutation (56.4%). This may reflect the clinical service and the population it serves. MIBG avidity was no different in tumours associated with a genetic predisposition compared to those negative for RET, VHL, and SDHx mutations. We suggest that MIBG uptake is measured pre-operatively in PHAEOs/PGLs where otherwise indicated, irrespective of genotype.