Hamartoma of mature cardiac myocytes presenting as a polypoid epicardial tumor in the interatrial groove and with gene fusions by copy number anomalies of chromosome 7

Hamartoma of mature cardiac myocytes (HMCM) is an extremely rare cardiac tumor characterized by benign growth of differentiated mature striated cardiac myocytes, and usually involves the ventricular myocardium. We describe the case of a 15-year-old female who presented with a short history of atrial fibrillation and a polypoid epicardial tumor that was attached to the interatrial groove by a short pedicle. The resected specimen showed features consistent with HMCM. Although these tumors are not associated with any known molecular or cytogenetic abnormalities, we identified fusions transcripts along with complex copy number anomalies of chromosome 7.