Unveiling the Unknown: A Case Report of Undifferentiated Pleomorphic Sarcoma in the Heart.

Undifferentiated pleomorphic sarcoma (UPS) of the heart is an exceedingly rare and highly aggressive tumor. We present the case of a 66-year-old male with a history of stage I prostatic acinar adenocarcinoma who was incidentally found to have a left atrial mass during cancer workup. Multimodal imaging (echocardiography, CMR, PET-CT) initially suggested a benign lesion. The patient underwent surgical excision of the mass, which revealed UPS confirmed by histopathology and immunohistochemistry. Postoperatively, the patient experienced right-sided heart failure, recurrent skin ulcers requiring grafting, and atrial arrhythmia. Despite complications, he stabilized and started chemotherapy and oncologic follow-up. This case highlights the diagnostic pitfalls of cardiac UPS, the necessity for tissue confirmation, and the role of coordinated multidisciplinary care.