This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Lung Tumor, Subject name: Pathology
[{'content': 'Which is the most common tumor associated with superior vena cava syndrome? \nSelect and explain. \nA. Lung cancer, B. Lymphoma, C. Metastasis, D. Thyroid cancer', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The superior vena cava syndrome usually is caused by neoplasms that compress or invade the superior vena cava, such as bronchogenic carcinoma or mediastinal lymphoma. -produces a characteristic clinical complex consisting of marked dilation of the veins of the head, neck, and arms associated with cyanosis. -Pulmonary vessels also can be compressed, causing respiratory distress.', 'role': 'assistant'}]