Unexpected diagnosis of metastatic breast carcinoma in an endomyocardial biopsy done for cardiac allograft rejection evaluation.

We report a case of a 75-year-old female post orthotopic heart transplantation, who presented to the emergency department with a six-week history of shortness of breath, hand tremor and ultimately delirium. She had lobular breast carcinoma more than 5 years prior to her heart transplant, treated by lumpectomy followed by anthracycline based chemotherapy. The reason for her heart transplant was heart failure that was suspected to be from anthracycline cardiomyopathy, however, her explanted heart actually showed cardiac sarcoidosis. She was placed on long-term immunosuppression with tacrolimus, mycophenolate mofetil and prednisone. Two years after her heart transplant, she underwent bilateral mastectomies for recurrent breast cancer. Her neurological workup, including brain imaging (CT, MRI, LP and EEG) did not show any structural abnormalities, ischemia, mass or neurosarcoidosis as cause for delirium. Tacrolimus was held due to renal dysfunction and hemolytic anemia, and then she developed signs of right heart failure so an endomyocardial biopsy was carried out for suspected allograft rejection. The biopsy did not show any evidence of cellular or antibody medicated rejection; however, it demonstrated infiltration by bland appearing cells with signet ring morphology cells many of which showed intracytoplasmic mucin. The cells were strongly positive with cytokeratins AE1/3, CK7 and mammaglobin. The morphology and immunoprofile were consistent with metastatic lobular breast carcinoma and this was thought to be the cause of her clinical presentation with delirium, hemolytic anemia and renal dysfunction as a paraneoplastic syndrome. (C) 2020 Elsevier Inc. All rights reserved.