To investigate the clinicopathological features and differential diagnosis of CIC-rearranged sarcoma (CRS).

Five CRSs of 4 patients (2 biopsies of pelvic cavity and lung metastasis from case 4) diagnosed in the First Affiliated Hospital of Nanjing Medical University were enrolled from 2019 to 2021. All cases were evaluated by clinical presentation, H&E, immunohistochemical staining and molecular analysis and the related literature was reviewed.

There were one male and three females, the age at diagnosis ranged from 18 to 58 (mean 42.5) years. Three cases were from the deep soft tissues of the trunk and one case from the skin of foot. Grossly, the tumor size ranged from 1 to 16 cm. Microscopically, the tumor was arranged in nodules or solid sheets. The tumor cells were typically round or ovoid, with occasional spindled or epithelioid morphology. The nuclei were round to ovoid with vesicular chromatin and prominent nucleoli. Mitotic figures were brisk (>10/10 HPF). Rhabdoid cells were seen in four of five cases. Myxoid change and hemorrhage were observed in all samples and two cases showed geographic necrosis. Immunohistochemically, CD99 was variably positive in all samples, while WT1 and TLE-1 were positive in four of five samples. Molecular analysis showed CIC-rearrangements in all cases. Two patients succumbed within 3 months. One had mediastinal metastasis 9 months after surgery. One underwent adjuvant chemotherapy and remained tumor-free 10 months after diagnosis.

CIC-rearranged sarcoma is uncommon and shows aggressive clinical course with dismal prognosis. The morphological and immunohistochemical characteristics can largely overlap with a variety of sarcomas; hence, knowledge of this entity is vital to avoid potential diagnostic pitfalls. Definitive diagnosis requires molecular confirmation of CIC-gene rearrangement.

Soft tissue neoplasms; Immunohistochemistry; Diagnosis, differential