This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
[{'content': "A 70 year old male presentes with breathlessness, facial swelling and dilated veins on the chest wall. The MOST common cause is: \nSelect and explain. \nA. Hodgkin's lymphoma, B. Thymoma, C. Lung cancer, D. Superior vena caval obstruction", 'role': 'user'}, {'content': 'Answer: D \nExplanation: Breathlessness, facial swelling and dilated veins on the chest wall, are features of Superior vena caval obstruction. Lung cancer, paicularly of small cell and squamous cell histologies, accounts for approximately 85% of all cases of malignant origin. In young adults, malignant lymphoma is a leading cause of SVCS. When SVCS is noted in a young man with a mediastinal mass, the differential diagnosis is lymphoma vs primary mediastinal germ cell tumor. Ref: Harrisons principles of internal medicine, 18th edition, Page: 2266', 'role': 'assistant'}]