Primary cardiac CIC‐rearranged undifferentiated sarcoma in an infant

INTRODUCTION: Cardiac neoplasms are particularly rare in children, and the majority of these tumors are benign. Approximately 10% of cardiac neoplasms are malignant, including soft tissue sarcomas and lymphomas. Cardiac tumors could also be metastases. Primitive EWSR1‐negative round or spindle cell undifferentiated sarcoma harboring CIC gene translocation is a highly aggressive malignancy mainly occurring in soft tissues. However, it has not yet been described in the heart. CASE PRESENTATION: We report a sarcoma that arose from the right ventricle in a 1‐year‐old girl. Histologically, it was composed of closely arranged small round or oval undifferentiated cells with fibrovascular separation, hyaline degeneration, and geographical necrosis. Immunohistochemically, the neoplastic cells exhibited focal membrane positivity for CD99 and diffuse positivity for WT1 and ETV4. Fluorescent in situ hybridization analysis showed EWSR1‐negative but CIC‐positive split signals. The breakpoint was also confirmed by whole genome sequencing. CONCLUSION: Based on morphological, immunohistochemical and molecular findings, this cardiac mass was diagnosed as CIC‐rearranged sarcoma.