A 40-year-old male with a history of pulmonary tuberculosis 20 years ago, previously healthy, has had an irritative cough for the past 3 months, occasionally with blood-streaked sputum and intermittent fever. Chest X-ray shows a 2cm × 2.5cm lobulated mass with irregular margins in the anterior segment of the right upper lobe. Three sputum cytology tests were negative. The most likely diagnosis is: