A 63 year old white man was referred to hospital with a two month history of left sided diffuse chest pain, weight loss, and progressive breathlessness on exertion. He was a retired joiner and had a 20 pack year history of smoking. He had not recently travelled abroad. He was taking bendroflumethiazide for hypertension.

On examination, his blood pressure and heart rate were normal, respiratory rate was 14 beats per minute, and oxygen saturation was 97% on air. He had no clubbing, pedal oedema, or lymphadenopathy. Respiratory examination showed dullness and reduced breath sounds in the left lower and middle zones. Cardiac and abdominal examinations were normal.

Chest radiography showed a moderate left sided pleural effusion, and electrocardiography was normal. Renal function, biochemistry, and bone profile were normal. Straw coloured pleural fluid was aspirated under ultrasound guidance; subsequent analysis showed total protein of 44 g/l (total serum protein 68 g/l), glucose 5.3 mmol/l, and lactate dehydrogenase 423 U/l, with no malignant cells or microbial growth.