An asymptomatic pleural mass in a 72-year-old man.

A72-year-old man scheduled for cardiac surgery presented for evaluation of an intrathoracic mass noted on a preoperative chest roentgenogram. He denied chest pain, dyspnea, cough, weight loss, or fever. In the 1950s, while working above ground with coal, the patient had a routine chest roentgenogram that showed a left pleural mass. He remained as-ymptomatic, however, and the mass enlarged only minimally during long-term observation. Ten years ago, the patient underwent cardiac bypass surgery but now required revascularization because of unstable angina. The patient was an exsmoker and denied exposure to asbestos or talc. Physical Examination Vital signs: normal, HEENT: unremarkable. Neck: no lymph nodes or thyromegaly. Chest: dullness and decreased breath sounds over the left posterior and lateral lung field. Cardiac: regular rhythm without murmurs. Abdomen: no organomegaly. Extremities: no clubbing or edema. What is the most likely cause of the chronic pleural mass?