neuroendocrine tumourAn endocrine tumour neoplasm with a characteristic morphology, often composed of sheets and clusters of round blue cells with granular chromatin and an attenuated rim of poorly demarcated cytoplasm.
NETs present with vague, nonspecific symptoms, including abdominal pain, nausea, weight loss and, rarely, obstructive symptoms; only 10% present with a carcinoid syndrome due to high circulating neuroendocrine hormones, in particular serotonin (5-HT), which causes flushing, diarrhoea, asthma and tricuspid regurgitation.
Carcinoids, small cell carcinomas, medullary carcinoma of thyroid, Merkel cell tumour, cutaneous neuroendocrine tumours, pancreatic islet cell tumours, pheochromocytoma.
Low grade—Typical carcinoid.
Intermediate grade—Atypical carcinoid.
High grade—Large cell: neuroendocrine tumour; small cell: lung cancer.