RADT-35. POSTOPERATIVE RADIOTHERAPY FOR WHO GRADE II–III INTRACRANIAL EPENDYMOMA IN ADULTS: AN INTERGROUP COLLABORATIVE STUDY (KROG 18-06/KNOG 18-01)

Abstract BACKGROUND To evaluate the impact of adjuvant postoperative radiotherapy (PORT) in adult WHO grade II–III intracranial ependymoma (IEPN). METHODS A total of 172 pathologically confirmed adult grade II–III IEPN patients from 12 institutions were eligible. Of them, 106 (61.6%) and 66 (38.4%) patients were grade II and III, respectively. For grade II and III IEPNs, 51 (48.1%) and 59 (89.4%) patients received PORT, respectively. The median dose to the primary tumor bed was 54.0 Gy and 59.4 Gy for grade II and III patients, respectively. The prognostic impact of sex, age, performance, WHO grade, location, size, surgical extent, and PORT on local control (LC), progression-free survival (PFS), and overall survival (OS) were evaluated by univariate and multivariate analysis. RESULTS The median follow-up period for survivors was 88.1 months. The 5-/10-year LC, PFS, and OS rates were 64.8%/54.0%, 56.4%/44.8%, and 76.6%/71.0%, respectively. On multivariate analysis, adjuvant PORT significantly improved LC (P=0.002), PFS (P=0.002), and OS (P=0.043). Older age (P< 0.001), WHO grade III (P< 0.001), larger tumor size (P=0.004), and lesser surgical extent (P< 0.001) were also negative factors for OS. Adjuvant PORT also improved LC (P=0.010), PFS (P=0.007), and OS (P=0.069) on multivariate analysis for grade II IEPNs. CONCLUSION This multicenter retrospective study supports the role of adjuvant PORT in terms of disease control and survival in adult grade II–III IEPNs. Prospective randomized trials focused on individualized treatment based on molecular subtypes is warranted.