Ectopic insulin secreting tumours are rare and infrequent. Presentation can be with recurrent or constant hypoglycaemia often in older patients with advanced cancer. The mechanism is through: insulin or insulin-like activity (IGF-2)(often termed non-islet cell tumour hypoglycaemia), reduced gluconeogenesis, disruption of glucagon metabolism, or utilisation of glucose by the tumour. Neuroendocrine tumours are recognised as having hypoglycaemic potential.
We describe a 73 year old male, presenting as an emergency with confusion and sweats. Pre-hospital glucose was < 1 mmol/mol. Following treatment, admission glucose was 1.8 mmol/mol. Past medical history and drug history were unremarkable. Clinical examination revealed a large irregular right upper quadrant mass. Staging CT revealed hepatic, lung and sclerotic bone metastases and a normal pancreas. Liver biopsy was arranged. Biochemistry revealed: a blood glucose of <0.1 mmol/L with inappropriately elevated insulin of 224.3 pmol/L and C-peptide of 1953 pmol/L, and IGF-1 of 25 ug/L. Glycaemia became difficult to manage with oral carbohydrate alone. Prednisolone was initiated at a dose of 40 mg daily, which initially controlled blood glucose. Rapid recurrent hypoglycaemia ensued and IV 10 % dextrose and oral diazoxide were required. Octreotide subcutaneously was also initiated. Tumour markers revealed a prostatic specific antigen levels of 82.7 ng/ml and Chromogranin A 16.5 ng/ml. Degarelix was commenced for presumed prostate adenocarcinoma, but sadly he did not wish for further intervention and withdrew consent for treatment. Liver biopsy revealed a large cell poorly differentiated neuroendocrine carcinoma (NEC).
Post-mortem revealed a liver effaced by multiple deposits with no remaining parenchyma and a normal pancreas and small bowel. Histology revealed a mixed small and non-small cell NEC in the left adrenal metastasis and a large infiltrated prostate containing well and poorly differentiated adenocarcinoma and high grade neuroendocrine small cell carcinoma. This to our knowledge is the first report of ectopic insulin secretion in association with a mixed disseminated high grade neuroendocrine carcinoma of the prostate.