- Per the American Joint Committee on Cancer (AJCC) 7th edition, pleural and pericardial are now considered stage M1a disease; when pleural fluid is visible on the computed tomography (CT) scan or on a chest x-ray, a thoracentesis is required to confirm that the pleural fluid is cytologically negative; patients with exudative pleural effusions are excluded, regardless of cytology; patients with effusions that are minimal (i.e. not visible on chest x-ray) that are too small to safely tap are eligible; a small effusion that has positive fludeoxyglucose F 18 (FDG) uptake on positron emission tomography (PET) has to be proven to be malignant per standard of care diagnostic procedures for the patient to be excluded