Endocrine Abstracts

Background: Phaeochromocytomas and paragangliomas (PPGLs) are histologically identical tumours that exhibit significant clinical heterogeneity. At least 40% of PPGLs arise due to the presence of a pathogenic germline variant (PGV) in a known susceptibility gene. PGVs affecting the mitochondrial enzyme succinate dehydrogenase (SDHA, SDHB, SDHC and SDHD) are the most common. Phenotypic features of PPGLs secondary to SDHB and SDHD PGVs are well documented and demonstrate a variability (tumour location, rates of catecholamine secretion, metastatic risk etc.) that is not currently understood. Due to their rarity the behaviour of SDHA related PPGLs are less well documented. Cascade screening is now offered to all patients with an SDHA PGV and so we can expect to encounter unaffected carriers more frequently in our clinical practice. Here we will discuss our experience of 18 index cases of SDHA related PPGLs and 10 relatives diagnosed as carriers via cascade screening.

Methods: Patients presenting with a PPGL with either a PGV or a VUS of SDHA were identified via our neuroendocrine tumour multidisciplinary team database. A retrospective chart review was carried out. An additional 14 SDHA PGV carriers were also identified via cascade screening (n=12) or via the 100,000 genome project (n=2).

Discussion: We report 18 cases (8F, 10M) of a PPGL related to an SDHA PGV (n=12) or VUS (n=6). Patients were aged 16-64 (median age of 40). 38.9% of PPGLs were found in the head and neck, 27.8% were abdominal PGLs, 11.1% were in the bladder, 11.1% presented as pheochromocytomas, 5.6% were found in the mediastinum and 5.6% had widespread metastatic disease at initial presentation. Catecholamine excess was diagnosed in at least 44.4% of cases. The most common presenting complaint was of swelling or symptoms related to tumour compression (44.4% of cases). Symptoms related to catecholamine excess were present in 33.3% of cases. 33.3% of this cohort went on to develop metastatic disease. Of the 14 patients identified as an SDHA PGV carrier, one patient was diagnosed with renal cell carcinoma (identified via the 100,000 genome project) but no patient identified via cascade screening went on to develop a PPGL.

Conclusion: The penetrance of disease in non-index cases of an SDHA PGV is low in this cohort. We also show a variability in tumour location and catecholamine production that is distinct from other SDHx related disease. In this small cohort there was a high rate of metastatic disease.