Cytological Features of CIC-rearranged Sarcoma. A Report of 5 New Cases and Review of the Literature.

Background CIC‑rearranged sarcoma is a rare, Ewing‑like round cell sarcoma and is poorly described in the cytology literature, with only seven cases reported to date. This report presents five new cases investigated and treated at the Institut Curie (four tumours showed CIC‑DUX4 and one showed CIC‑NUTM1 fusions) and reviews corresponding cytological literature. Summary Smears were cellular in all cases. They comprised of isolated and clustered round, oval and short spindle cells, with rosettes in three cases. Cytoplasm varied in volume and occasionally showed microvacuolation. Marked pleomorphism and rhabdoid features were detected in one CIC-NUTM1 sarcoma and in one CIC-DUX4 sarcoma cases. CD99 was positive in three cases and negative in two. Original cytologic diagnoses included two round cell sarcomas (one with myxoid features), pleomorphic sarcoma with rhabdoid features, Ewing sarcoma, and rhabdomyosarcoma. Key messages Fine‑needle aspiration appears to be at least as effective as core-needle biopsy for these malignancies. Cytomorphological features, together with the immunohistochemical profile and detection of CIC rearrangements, can help accurately diagnose this rare malignancy.