PLAB-0896

A 60-year old male presented to the OPD with a complaint of a rusty-coloured sputum along with a cough for 3 days. His has a history of smoking for 40 years, and a history of significant weight loss. His chest X-ray revealed solid nodules in both lungs and bilateral hilar lymphadenopathy. Out of the following, which one is the most appropriate investigation?