oat cell carcinoma see small cell carcinoma .

oedema [oe-de-ma] Swelling caused by an excessive accumulation of fluid in the tissues of the body, i.e. outside the circulatory system.

oesophageal cancer [oe-soph-a-ge-al can-cer] Cancer of the oesophagus . The most common symptom is difficulty swallowing.

oesophagus [oe-soph-a-gus] The gullet; the tube that connects the throat with the stomach , down which food passes.