A 52-year-old male smoker with a 30-year history of cigarette use presents with persistent cough and hemoptysis. Chest X-ray shows a mass in the left lower lobe. Bronchoscopy reveals a reddish, friable lesion in the left main bronchus. The bronchial mucosa appears abnormal with loss of normal ciliated columnar epithelium. Which investigation is most appropriate to confirm the diagnosis of squamous metaplasia with dysplasia?