A form of lung cancer. Small cell carcinoma, also known as oat cell carcinoma, is characterized by cells that are small and round or oval and look like oat grains when seen under a microscope. It is the most aggressive type of lung cancer and is usually found in people who smoke or used to smoke. Common symptoms include a chronic cough, blood in the sputum, wheezing, repeated episodes of pneumonia, fever, weakness, weight loss, and chest pain. Advanced disease may also include hoarseness, shortness of breath, enlarged lymph nodes in the neck, pain in the arm and shoulder, difficulty swallowing, and drooping eyelids.