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
Which is the most common tumor associated with superior vena cava syndrome? 
Select and explain. 
A. Lung cancer, B. Lymphoma, C. Metastasis, D. Thyroid cancer
A: Lung cancer
Answer: A: Lung cancer 
Explanation: 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.