An adult presents to a physician because of repeated episodes of fainting. EKG fails to disclose an arrhythmia. Echocardiogram shows a mass in the left atrium that is acting like a "ball valve" to produce intermittent obstruction of flow. Which of the following would most likely be seen on microscopic examination of the resected mass?
Benign myxoid tumor Benign tumor with gland formation Benign tumor with striated muscle differentiation Malignant tumor with gland formation