Right Atrial Mass Secondary to Breast Cancer Metastasis

We present the case of a 42-year-old female with a history of human epidermal growth factor 2 (HER2) receptor-positive breast cancer status post bilateral mastectomy with metastasis to the spine and to the brain, who underwent transesophageal echocardiography (TEE) after outpatient transthoracic echocardiography (TTE) was suggestive of right atrial thrombus in transit. TEE revealed an atrial mass with a pedunculated stalk attached to the inferior right atrium near the inferior vena cava with a necrotic center. These findings were suggestive of an endocardial metastatic mass secondary to her primary breast cancer. The pericardium is the most common site of cardiac metastasis; meanwhile, endocardial involvement is infrequent, occurring in less than 5% of all cardiac metastases. Right atrial masses may cause evidence of right heart failure and thromboembolism of the pulmonary arteries. Treatment focuses on targeted chemotherapy, radiation therapy, and interventions as indicated. In this case, following the diagnosis of a right atrial mass, the patient was discharged the same day to begin outpatient chemotherapy.