A 56-year-old woman with a history of breast cancer surgery 5 years ago, followed by 6 months of chemotherapy. Six months ago, left supraclavicular lymphadenopathy was noted. For the past 2 months, she has experienced chest tightness and shortness of breath. Laboratory tests show: Hb 109g/L, WBC 6×10<sup>9</sup>/L, erythrocyte sedimentation rate (ESR) 40mm/hr. Chest X-ray reveals a right lung mass shadow and cardiomegaly with bilateral enlargement and weakened cardiac pulsations. The simplest and most feasible diagnostic method is: