Dyspnea After Liver Transplant: What’s Taking His Breath Away?

A 66-year-old male with a past medical history of primary biliary cholangitis s/p orthotopic liver transplant 10 months ago, ESRD s/p kidney transplant 2 months ago, presents with shortness of breath and dyspnea on exertion. His symptoms have gradually worsened over 2 weeks, and he is now short of breath walking across a room. He denies fevers, chills, and sick contacts. He is compliant with his medications and currently on prednisone, mycophenolate mofetil, and tacrolimus for immunosuppression. Liver chemistries are within normal limits and chest imaging shows a large right pleural effusion and right anterior chest wall mass. What is the most likely underlying diagnosis?