UPDATE, Aug 8: The El Paso Medical Examiner's Office has determined that Sherman suffered from "super vena cava syndrome." The syndrome was a result of lung cancer. The ME found a "mass" on the actor's lung. According to the National Cancer Institute, superior vena cava syndrome occurs when the superior vena cava -- one of the body's major veins -- is obstructed, most commonly because of a cancer or tumor. The superior vena cava is responsible for returning blood to the heart that comes from the upper part of the body.