Clinical characteristics and outcomes for children,adolescents and young adults with “CIC-fused” or “BCOR-rearranged” soft tissue sarcomas. A multi-institutional European retrospective analysis

Background: In certain rare undifferentiated small round cell sarcomas new specific molecular CIC-DUX4/other partner, BCOR-CCNB3/other partner, YWHAE fusions, or BCOR-ITD (internal tandem duplication) were identified. These new "CIC fused" (CIC-fused/ATXN1::NUTM1) and "BCOR rearranged" (BCOR fused/ITD/ YWHAE) soft tissue sarcomas (STS) are not well described. Methods: Multi-institutional European retrospective analysis of young patients (0-24 years) with CIC-fused and BCOR rearranged STS. Results: Overall, out of the 60 patients selected, the fusion status was CIC-fused (n = 29), ATXN1::NUTM1 (n = 2), BCOR::CCNB3 (n = 18), BCOR-ITD (n = 7), and YWHAE (n = 3), MAML::BCOR STS (n = 1). The main primaries were abdomen-pelvic (n = 23) and limbs (n = 18). Median age was 14 years (0.9-23.8) and 0.9 (0.1-19.1) for CIC-fused and BCOR-rearranged groups, respectively (n = 29; p < 0.001). IRS stages were I (n = 3), II (n = 7), III (n = 35), and IV (n = 15). Overall, 42 patients had large tumors (>5 cm) but only six had lymph node involvement. Patients received mainly chemotherapy (n = 57), local surgery (n = 50), and/or radiotherapy (n = 34). After a median follow-up of 47.1 months (range, 3.4-230), 33 (52%) patients had an event and 23 patients died. Three-year event-free survivals were 44.0% (95% CI 28.7-67.5) and 41.2% (95% CI 25.4-67.0) for CIC and BCOR groups (p = 0.97), respectively. Three-year overall survivals were 46.3% (95% CI 29.6-72.4) and 67.1% (95% CI 50.4-89.3; p = 0.24), respectively. Conclusions: Pediatric patients often present with large tumors and metastatic disease, especially CIC sarcomas. Overall outcome is dismal. New treatment options are needed.