Neuroendocrine tumours (NETs) are a broad group of complex tumours that arise from neuroendocrine cells.
NETs which occur in the lungs, bronchi, thymus, small intestine, appendix or rectum, and pancreatic neuroendocrine (PNET or PET) tumours, which arise in the endocrine tissues of the pancreas.
NETs may also arise in the parathyroid, adrenal and pituitary glands, as well as in speciﬁc cells of the thyroid.
Less frequently, NETs may also occur in the ovaries, cervix, testicles, spleen and breast but these are considered very rare.
NETs are classiﬁed as being functional or non-functional.