An indolent course of undifferentiated pleomorphic cardiac sarcoma mimicking myxoma: A case report.

Cardiac undifferentiated pleomorphic sarcoma (UPS) is a rare and highly malignant tumor, commonly arising in the left atrium. It is associated with poor prognosis, nonspecific symptoms, and difficulty in early diagnosis. Here, we report a case of a 71-year-old woman who presented with palpitations, chest pressure, and exertional dyspnea, in whom initial cardiac magnetic resonance imaging revealed only subtle atrial septal thickening, evaluated as nonspecific, whereas follow-up imaging 2 years later showed progressive growth, ultimately interpreted as a cardiac myxoma. Surgical resection was performed, and histopathologic examination revealed a high-grade UPS with immunohistochemistry and molecular profiling supporting the diagnosis, including amplification of MDM2 and PDGFRA. No metastases were detected, and after multidisciplinary discussion a decision was made to abstain from adjuvant therapy. This case highlights the diagnostic challenge posed by cardiac UPS mimicking benign tumors such as myxoma on imaging and the importance of longitudinal imaging review and a high index of suspicion in cases with atypical radiological features of myxoma. It also raises awareness of an unusually indolent behavior of an UPS that otherwise pursues an aggressive course.