CIC-Rearranged Sarcoma: A Clinical and Pathological Study of a Peculiar Entity

Background: CIC-rearranged sarcoma is a rare and aggressive type of undifferentiated round cell tumor characterized by CIC gene fusion, most commonly CIC::DUX4. This study presents a series of eleven cases, highlighting their clinicopathological features. Methods: Pathology records (2019 to 2024) were searched using "sarcoma with CIC", identifying eleven cases, of which seven referred cases were initially misdiagnosed. Pathological and clinical analysis was conducted. Treatment was dictated upon multidisciplinary panel discussion based on tumor stage. Follow-up data (1-25 months) was available for all patients. Results: The cohort included six males and five females, with a median age of 43 years (range;14-53), with nine in soft tissue and two in bone. Tumor size ranged from 3.5 cm to 20.0 cm (mean: 9.8 cm). Most cases showed sheets of undifferentiated round- to oval-shaped cells. Two cases showed an Ewing-like pattern, and one case showed spindle cells in a fibrotic stroma transitioning to epithelioid cells. Necrosis was present in nine cases, and mitotic count ranged from 2 to 38/ 10HPFs (mean = 14.2). CD99 was positive in (10/11) cases and WT-1 in (6/9). NKX2.2, S100, and MDM2 were positive in rare cases. CIC::DUX4 fusion was detected in four cases. FISH for CIC gene rearrangement was positive in seven cases, two of them confirmed by methylation analysis. Metastasis at diagnosis was common (n = 8), primarily in the lungs, with later metastasis to the brain and bone. At time of final analysis, eight patients died within a median of 10 months (range: 1-19 months), while three were alive, two with stable disease (for a period of 6 and 25 months) and one with progression after 10 months. Significant correlation was seen between overall survival and the presence of metastasis at diagnosis (p value = 0.03). Conclusions: CIC-rearranged sarcomas are rare, high-grade tumors with predilection for soft tissue. Misdiagnosis is frequent, necessitating molecular confirmation. These tumors are treatment-resistant, often present with lung metastasis, and carry a poor prognosis, especially with initial metastasis.