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The forgotten neoplasia of MEN-1 syndrome: thymic neuroendocrine tumours

E Mills, S Wijetilleka, R Agha-Jaffar, J Anderson, JF Todd, Hammersmith Hospital, Imperial College Healthcare NHS Trust

Introduction: Multiple endocrine neoplasia type 1 (MEN-1) is an autosomal dominant condition with tumours which mainly affect the parathyroid glands, pancreatic islets and pituitary gland.  Patients are regularly evaluated to detect associated tumours with the aim of improving survival and quality of life. 

Case presentation: We report a 39-year man with a history of MEN-1, which was diagnosed in 2008, when aged 30-years he presented with primary hyperparathyroidism requiring a two-gland parathyroidectomy.  A 7-mm microprolactinoma was detected in 2012 and he remains on Cabergoline 0.5mcg three times weekly.  In 2009, he presented with hypoglycaemia from an insulinoma, along with elevated gastrin levels from a gastrinoma, requiring surgical enucleation of two pancreatic tail lesions (February 2009), followed by a spleen preserving distal pancreatectomy (April 2009) for persistent and symptomatic hypoglycaemia.  However, post-operatively gut hormones remained elevated and two further gallium avid lesions became apparent on Gallium-68 DOTATATE PET CT.  The Neuroendocrine Tumours MDT offered a total pancreatectomy, which he declined.  He has been referred for consideration of radio-frequency ablation to these tumours.

However, in June 2017, surveillance Gallium-68 DOTATATE PET CT for the pancreatic tumours, also demonstrated a new gallium avid lesion within the anterior mediastinum.  Corresponding, CT thorax proved this activity to originate within the thymus.  He therefore underwent a thymectomy via a video-assisted thoracoscopic approach.  Histology confirmed a grade 2 thymic neuroendocrine tumour with Ki-67 proliferation index of 15%, tumour cells expressing CD56 and synaptophysin, and widespread lymphovascular invasion.  Given that the tumour was present at the surgical margin and the other high-grade features, he is high-risk for recurrence and a 4-month post-operative Gallium-68 DOTATATE PET CT is planned.  In addition, he has started somatostatin analogue therapy.

Discussion: Thymic neuroendocrine tumours, an uncommon manifestation of MEN-1, are rare neuroendocrine tumours with an estimated prevalence of 2-5%.  They are commonly asymptomatic with a mean age at diagnosis of 42.7 years and occur almost exclusively in men.  Current guidelines recommend CT or MRI chest imaging every 1-2 years with imaging universally positive at diagnosis.  Although uncommon, they remain an important component of MEN-1 due to being a major determinant of life expectancy.  Due to aggressive behaviour, they have an estimated 10-year survival rate of 25-45%.  Surveillance therefore remains essential.