Abstract
Carcinomatous pericarditis is a rare complication of locally aggressive breast cancer in which malignant cells directly extend into the pericardium causing inflammation and creating a pericardial effusion. A 40-year-old woman with untreated metastatic breast cancer presented to an outpatient clinic in significant distress with symptoms of progressive shortness of breath and bilateral leg swelling. An urgent echocardiogram demonstrated a large pericardial effusion with echocardiographic evidence of cardiac tamponade. She underwent emergent pericardiocentesis of the effusion that was deemed to be malignant after cytologic evaluation. Subsequently, she opted for palliative treatment involving the surgical creation of a right pericardial window and placement of an indwelling pleural catheter. Internists should maintain a high index of suspicion for malignant cardiac tamponade in at-risk patients, especially those with locally aggressive and advanced malignancies.