MDB-03. Medulloblastoma at Relapse: For Which Patients and Which Tumors Reirradiation Is the Better Choice

Abstract BACKGROUND First-line therapies for medulloblastoma(MBL) are obtaining higher survival-rates while decreasing late-effects, but treatment at relapse is not yet standardized. We report the experience with MBL re-irradiation(re-RT), its timing and outcome in different clinical settings and tumor groups. METHODS Patient’s staging/treatment at diagnosis, histotypes/molecular subgroups, relapse site/s, re-treatments outcome are reported. RESULTS Between 2002 and 2019, relapsing patients were 25, median age at diagnosis 11.4 years, 8 had metastases, three LC/A histotype. According to 2016-2021 WHO-classification, 14 had SHH subgroup tumors (6 TP53 mutated,1 + MYC and 1 + NMYC amplification), 11 non-WNT/non-SHH (2 with MYC/MYCN amplification). Thirteen had received HART-CSI, 11 standard-CSI, one HFRT; all post-radiation chemotherapy(CT), 16 also pre-RT. Median time to relapse (local-LR in 9, distant-DR in 14, LR+DR in two) was 26 months. Fourteen patients were re-operated, in 5 excising single DR-sites, thereafter 3 received CT, two after re-RT; out of 11 not re-operated patients, 4 had re-RT as first treatment and 7 after CT. Re-RT was administered at median 32 months after first RT: focally in 20 cases, CSI in 5, never resulting in radionecrosis. Median post-relapse-PFS/after re-RT were 16.7/8.2 months, while overall survival-OS were 35.1/23.9 months, respectively. Metastatic status both at diagnosis/relapse negatively affected outcome and re-surgery was prognostically favorable. MYC,MYCN,P53 status and molecular subgroups, RT extension/fractionation, gender and age were not statistically prognostic; in the multivariable model, OSs were positively influenced by longer intervals before re-RT, re-surgery and not-SHH subgroups (P=0.019 from recurrence and 0.004 from second RT). CONCLUSIONS Re-surgery + reRT can prolong survival; a substantial fraction of patients with worse outcome belonged to SHH-subgroup.