A man, aged 64, complains of cough with sputum discharge, sometimes with blood spitting. Smokes during 30 years. In the last 3 months has lost 8 kg. On roentgenologic examination in the middle lobe of the right lung there is a cavernous formation, the inner outline is irregular, contains a small quantity of fluid, on the right the central lymph nodes are enlarged. What examination is the most informative to define the diagnos