A 60 year old male presented to the emergency with breathlessness, facial swelling and dilated veins on the chest wall. Which of the following is the most common cause?

Patient in the question is showing signs and symptoms typical of superior vena caval obstruction which result in severe reduction in venous return from the head, neck, and upper extremities. Most common causes includes lung cancer, lymphoma, and metastatic tumors. 85% of cases occur due to small and squamous cell carcinoma of the lung. In young adults, malignant lymphoma is a leading cause. Other causes include benign tumors, aoic aneurysm, thyromegaly, thrombosis, and fibrosing mediastinitis from prior irradiation, histoplasmosis, or Behcet's syndrome. Ref: Harrsions Internal Medicine, 18th Edition, Chapter 276