A 64-year-old woman presents with 6 weeks of fatigue, dyspnea, and night sweats. She has lost 11 lb. She has no history of trauma, has never had surgery, and takes no medications. Chest x-ray reveals a large right-sided pleural effusion. Thoracentesis yields pleural fluid that appears milky. Pleural fluid triglyceride level is 500 mg/dL. Which of the following disorders is most likely in this patient?