A 31-year-old woman is referred for investigation of a left lower lobe mass. She was well until 1 year earlier when she acquired a persistent unproductive cough. She ignored this symptom until 7 months ago when, after a respiratory tract infection with significant worsening of symptoms, she finally sought medical attention. While the systemic symptoms improved after antimicrobial therapy, her cough persisted. She received two further courses of antibiotics because of cough and an abnormality noted in the left lower lobe of the lung, which was thought to represent an infectious pneumonia.