Which of the Following Leads to the Greatest Percentage of Superior Vena Cava Syndrome Cases?

The Answer

The greatest percentage of cases of superior vena cava syndrome is caused by C. Non-small cell lung cancer.

The greatest percentage of superior vena cava syndrome cases (https://www.ons.org/books/understanding-and-managing-oncologic-emergencies-resource-nurses-third-edition) are caused (in descending order) by non-small cell lung cancer, small cell lung cancer, and non-Hodgkin lymphoma. Superior vena cava syndrome is often the presenting condition which leads to those cancer diagnoses. 

Less common causes include thyroid cancer, melanoma, Kaposi sarcoma, and tuberculosis.