Background. Malignant carcinoid syndrome is the constellation of symptoms typically exhibited by patients with metastases from carcinoid tumors. This syndrome is characterized by hot, red flushing of the face; severe and debilitating diarrhea; and asthma attacks.Malignant carcinoid syndrome occurs in fewer than 10% of patients with a carcinoid tumor.Carcinoid tumors arise from neuroendocrine cells, which are widespread in the human body, especially in the organs derived from the primitive intestine.See the image below.his syndrome is characterized by hot, red flushing of the face; severe and debilitating diarrhea; and asthma attacks. Malignant carcinoid syndrome occurs in fewer than 10% of patients with a carcinoid tumor.