<prompt> Which is the most common tumor associated with superior vena cava syndrome?Lung cancerLymphomaMetastasisThyroid cancer  <response>: 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. 