Primary CIC-DUX4 round cell sarcoma of the kidney: A treatment-refractory tumor with poor outcome

The CIC-DUX4 sarcoma is a subset of the undifferentiated small round cell sarcoma family, presently recognized as a new clinicopathological entity. It is a rare and highly aggressive tumor usually arising in the soft parts of the limbs and the trunk. Only a very few cases of primitive visceral CIC-DUX4 have been hitherto described. We report the case of a 29 year-old male patient with a primary CIC-DUX4 sarcoma of the kidney with lung metastasis. The outcome of the disease was rapidly unfavorable. Despite radical nephrectomy, the patient experienced an early local retroperitoneal recurrence associated with lung and liver metastases. The tumor did not respond to four successive lines of chemotherapy nor to palliative radiotherapy. Due to partial morphologic and immunohistochemical overlap with Ewing sarcoma, CIC-DUX4 positive tumors have generally been considered as Ewing-like sarcomas and managed similarly. However, this tumor shows a high propensity to metastasize and is much less sensitive to chemotherapy than Ewing sarcomas. The management of this type of very aggressive sarcoma needs to be defined by comprehensive biological and clinical studies.