Poster Presentation ESA-SRB-APEG-NZSE 2022

Introduction: Clinically silent phaeochromocytoma (PCC) are increasingly recognized but are typically small with relatively low levels of metanephrines. However, upregulation of catechol-O-methyltransferase (COMT), the enzyme that inactivates catecholamines to their metabolites in PCC, can cause clinical silence despite significant size and biochemical activity demonstrated by elevated metanephrine and normetanephrine levels. Composite PCC comprise PCC and a second tissue sharing embryological origin from the neural crest, including ganglioneuroma. While fewer than 100 cases have been described, they demonstrate similar natural history and prognosis to other PCC. Composite tumours are less frequently associated with most germline mutations causing PCC but more strongly associated with neurofibromatosis type 1.

Case: We present a 62-year-old woman with a clinically silent giant PCC, incidentally discovered on investigation for pulmonary embolism. Further imaging revealed a 15 cm adrenal mass and a second 7 cm pelvic mass. Prior to endocrine referral a biopsy of the adrenal mass suggested neuroblastoma. No haemodynamic compromise ensued with biopsy. Biochemical findings summarised in Table 1 confirmed a PCC with metanephrine excretion 23-fold normal despite normal catecholamines. The patient has no clinical or familial features of NF1 or other hereditary syndromes associated with PCC.

Surgical resection was uneventful after 6 months anticoagulation and preoperative alpha blockade. Histopathology showed a composite PCC/ganglioneuroma with discrete areas of both tumours within the same mass. Metanephrines and normetanephrines normalised 6 weeks post-operatively and have remained normal. Later resection of the pelvic mass revealed an unrelated ovarian teratoma. Genetic testing is yet to be performed as she does not qualify by local criteria.

Conclusion: Extreme activity of COMT, beyond typical for PCC, is likely to have caused intratumoural inactivation of catecholamines and facilitated asymptomatic growth of this tumour to its giant size. Composite PCC are rare but have a similar clinical presentation and management to other phaeochromocytoma.