[CIC-rearranged sarcoma with rhabdoid features: a clinicopathological analysis]

Objective: To investigate the histopathologic, immunohistochemical, molecular genetic characteristics of CIC-rearranged sarcoma (CRS) with rhabdoid features. Methods: The clinical and pathologic data of two cases of CRS diagnosed between 2019 and 2021 at the Department of Pathology, Jiangsu Province Hospital were analyzed. Immunohistochemical study and fluorescence in situ hybridization (FISH) were performed. The relevant literature was reviewed. Results: Both patients were female, one was 58 years old, with tumor located in left thigh; the other was 43 years old, with tumor located in left pelvic cavity. Microscopically, both tumors were composed of small to medium-sized round, oval cells, arranged in nodules or sheets. The tumor cells showed irregular nuclear outline, coarse chromatin with prominent nucleoli and brisk mitotic activity. Both cases showed rhabdoid phenotype with myxoid stromal changes. Immunohistochemically, both cases were positive for CD99 and c-myc. High WT1 reactivity was seen in classic area, with low reactivity in rhabdoid area. There was no INI1 lost in both cases. Both were negative for NKX2.2 and NKX3.1. By FISH both cases demonstrated convincing break-apart signals of CIC gene. One patient died of disease after 1 month, and the other died of disease after 3 months. Conclusions: CRS is a small round cell undifferentiated sarcoma of the bone and soft tissue defined by molecular genetic characteristics, and may show atypical morphologic and immunophenotypic characteristics such as rhabdoid features. A correct understanding of its rare morphologic and immunophenotypic characteristics, combined with molecular pathologic detection, is conducive to correct diagnosis.