Incidence of serotonin secretion in pancreatic neuroendocrine tumours

I wanted to confirm how uncommon this scenario was and found this study from some of the world’s most respected NET experts who work in one of the world’s most respected NET centres of excellence.  This is backed up by another document referred below (Reference 1).

It’s known that serotonin can be elevated but not sufficiently to cause symptoms or carcinoid syndrome, which is true of many hormonal issues with most NETs.  It’s also known that many cases of carcinoid syndrome do not manifest until there are liver metastases (or less common scenarios as described below).

According to Reference 1, Carcinoid syndrome occurs when biologically active amines and peptides enter the systemic circulation escaping the first-pass metabolism of the liver. Normally, these bioactive products are inactivated by the liver. However, in cases of neuroendocrine tumours with liver metastasis, either these bioactive products are directly released into the systemic circulation, or they escape inactivation due to deranged liver function.  Less commonly, carcinoid syndrome can occur without liver metastasis in conditions like a primary gut tumour with extensive retroperitoneal nodal metastases, a bronchial or ovarian NET, where it’s possible for bioactive amines to be released directly into the systemic circulation. 

According to Reference 2 below, elevated serotonin is possible in pancreatic NETs (7.8%) but only 0.8% were also diagnosed with carcinoid syndrome.