Endocrine Abstracts

Introduction: Pheochromocytoma and Paraganglioma (PPGL) are neuroendocrine tumours arising from chromaffin cells in the adrenal medulla or ganglia in the autonomic nervous system. ~40% of PPGL arise due to germline mutation (commonly SDHx) and sporadic tumours frequently have causative somatic mutations. 15-20% of PPGL behave in a malignant manner. ~95% PPGL express somastostatin receptors and are GaDOTATATE avid. Lutathera® is a commercially available PRRT. There is little known about the effectiveness of PRRT in PPGL. This report summarises our experience with PRRT in malignant PPGL.

Methods: Using electronic patient records, radiological, biochemical and clinical behaviour of metastatic PPGLs treated with PRRT (typically 4 cycles, 7.4GBq 177-Lutetium Dotatate) was documented.

Patient characteristics and key findings: Twelve patients were treated for metastatic PPGL, 9 of whom had a known tumour syndrome, 8 of which were SDH- mutation-related. 66% were secretory. Commonest sites of metastases were bone and lung. Mean duration of follow up after PRRT was 18 months. Five patients demonstrated stability at a range of 6 to 50 months, one of whom demonstrated features of regression at 6 months. Three patients progressed at 3 months and were referred for alternative treatment. Two have not yet undergone post-treatment surveillance imaging. One patient had grade 1 CTCAE criteria for toxicity after third cycle due to marrow suppression, with full recovery at twelve-months (1). There was no indication of renal impairment.

Limitations: This was a small series without a control group.

Conclusion: PRRT is well tolerated therapy. In this cohort of patients, with a mean of 18.8 months of surveillance, 42% showed stability. As clinical experience increases, NETTER-P will hopefully inform practice in terms of where PRRT is best placed in the malignant PPGL treatment algorithm (2).1 CTCAE v5.0 US Department of Health and Human Services, Nov 2017.2 NETTER-P Study ongoing-NCT04711135.