Yellow, cancerous tumors of hormone-making cells in the gastrointestinal tract (specifically, they are classed as neuroendocrine or amine precursor uptake and decarboxylation tumors). They produce excess endocrines such as kallikrein (an activator of bradykinin release) and serotonin. These tumors can be found in the intestine, stomach, or sometimes on the liver. In later stages, this type of cancer causes symptoms such as diarrhea, wheezing, heart murmurs, enlarged liver, and a dusky appearance to the skin. Carcinoids can be diagnosed with a urine test or with a CAT scan.