Background: This study aims at clarifying the impact of persistent residual lesions following first-line treatment for pediatric medulloblastoma.

Methods: Data on 84 pediatric patients with medulloblastoma and persistent residual lesions on centrally reviewed magnetic resonance imaging (MRI) at the end of first-line therapy were analyzed.

Results: Twenty patients (23.8%) had residual lesions in the tumor bed (R+/M0), 51 (60.7%) had distant lesions (R0/M+) and 13 (15.5%) had both (R+/M+). Overall response to first-line therapy was minor or partial (≥ 25% reduction, minor response [MR]/PR) for 64 (76.2%) and stable disease (SD) for 20 patients (23.8%). Five-year post-primary-treatment progression-free (pptPFS) and overall survival (pptOS) were superior after MR/PR (pptPFS: 62.5 ± 7.0%[MR/PR] vs. 35.9 ± 12.8%[SD], P = .03; pptOS: 79.7 ± 5.9[MR/PR] vs. 55.5 ± 13.9[SD], P = .04). Furthermore, R+/M + was associated with a higher risk for progression (5-year pptPFS: 22.9 ± 17.9%[R+, M+] vs. 72.4 ± 12.0%[R+, M0]; P = .03). Watch-and-wait was pursued in 58 patients, while n = 26 received additional treatments (chemotherapy only, n = 19; surgery only, n = 2; combined, n = 3; valproic acid, n = 2), and their outcomes were not superior to watch-and-wait (5-year pptPFS: 58.5 ± 7.7% vs. 51.6 ± 10.7% P = .71; 5-year pptOS: 76.3 ± 6.9% vs. 69.8 ± 9.7%, P = .74). For the whole cohort, 5-year pptPFS by molecular subgroup (58 cases) were WNT: 100%, SHH: 50.0 ± 35.4%, group-4, 52.5 ± 10.5, group-3 54.2 ± 13.8%; (P = .08).

Conclusions: Overall response and extent of lesions can function as surrogate parameters to predict outcomes in pediatric MB patients with persistent lesions after first-line therapy. Especially in the case of solitary persistent medulloblastoma MRI lesions, additional therapy was not beneficial. Therefore, treatment response, extent/kind of residual lesions and further diagnostic information need consideration for indication of additional treatments for persisting lesions.