Lexicon Pharmaceuticals (LXRX) shares are up nearly 50% since it announced Monday that its carcinoid syndrome drug telotristat etiprate met its primary endpoint in a late stage clinical trial. Lexicon CEO Lonnel Coats said the positive result is the biggest advance in treating patients of this rare cancer in 16 years. 'We go inside the cell and try and shut down the serotonin production so what you end up with is a complementary effect between the standard of care and putting telotristat etiprate on top of standard of care,' said Coats. 'So you get a better outcome for patients who become uncontrolled so they can go back to having more of a normal life.' Carcinoid syndrome is a rare disease affecting patients with neuroendocrine tumors that originate in the gastrointestinal tract and metastasize or spread to the liver or other organs. Overproduction of serotonin within these metastatic neuroendocrine tumor cells is a driver of carcinoid syndrome, which is characterized by debilitating diarrhea, facial flushing, abdominal pain and heart valve damage.