Non-islet cell tumour hypoglycaemia in a patient with a well-differentiated gastric neuroendocrine tumour.

A 61-year-old man, without noteworthy medical history, presented with complaints of progressive fatigue and flushes. Diagnostic imaging revealed a large tumour in the stomach with liver metastases, and histopathological examination showed a well-differentiated gastric neuroendocrine tumour (NET). After chemotherapy, everolimus was administered, and upon progression, PD-1 inhibitor PDR001 was started. Two weeks after the first gift, he was admitted with loss of consciousness and a blood glucose level of 1.6 mmol/L. Plasma insulin was below 0.5 mU/L, C-peptide level was 250 pmol/L, insulin-like growth factor (IGF)-II was 804 ng/mL, and pro-IGF-IIE level was 80 µg/L. Based on the clinical findings, the patient was diagnosed with non-islet cell tumour hypoglycaemia (NICTH) with an overproduction of pro-IGF-IIE and eventually IGF-II due to progressive metastatic well-differentiated gastric NET. NICTH is a very rare condition. It has been reported in several tumour types but has never been described as a consequence of NET.