Carcinoid tumours describe a range of neoplasms arising from neuroendocrine cells or their precursors. Of intestinal carcinoids, the most common sites are in the midgut, especially the appendix and terminal ileum. Non-intestinal carcinoids include those of the lung, testes and ovary. They are usually of low-grade malignancy.
The carcinoid syndrome develops when products, chiefly serotonin, are released by the tumour in large amounts and escape hepatic degradation.
The carcinoid syndrome is seen in two situations:
- intestinal carcinoids with hepatic metastases:
- the metastases reach sizes several times larger than that of the primary tumour and secrete products into the hepatic vein
- the vasoactive tumour products are able to enter the systemic circulation
- extra-intestinal carcinoids
Epidemiological studies from the US suggest the age-adjusted incidence of carcinoid tumours varies between 2.47 and 4.48 per 100,000 population, with the rates being highest in black males, then black females, then white Americans (1)
- population corrected male-to-female ratio for all carcinoid sites was 0.86
- average age at diagnosis for all carcinoid tumours was 61.4 years (compared with 63.9 years for non-carcinoid tumours)