Symptoms. Carcinoid tumors may not show any signs until the cancer is well advanced. When symptoms appear, they are often vague and depend on whether the cancer is in the digestive tract or the lungs. Symptoms of carcinoid tumors of the gastrointestinal tract include stomach pain, loose stools, nausea, vomiting, bleeding from the rectum, redness and flushing of the face. Lung carcinoids can cause chest pain, difficulty getting enough air, loose stools, facial redness and flushing, weight gain around the upper torso, and skin marks that look like pink or purple stretch marks.