MDB-92. Effect of Reduced-Dose Craniospinal Irradiation and Reduced-Dose Adjuvant Chemotherapy on Children and Adolescents With WNT Medulloblastoma Without Residual or Metastatic Disease: Results From the Sjmb12 Clinical Trial

Abstract BACKGROUND In response to studies showing medulloblastoma (MB) survival is not only contingent on clinical factors (e.g. metastases, residual disease) but also on molecular factors (e.g. molecular group, gene aberrations), we launched the SJMB12 (NCT01878617) trial to stratify treatment using both clinical and molecular risk factors. Specifically, we sought to evaluate if patients with WNT-group MB, without metastatic (M0) or residual disease (R0), treated with reduced-dose craniospinal irradiation (CSI) and reduced-dose cyclophosphamide-based chemotherapy could maintain a high survival with fewer treatment-related side effects. METHODS Tumors were molecularly stratified via immunohistochemistry and fluorescence in-situ hybridization. Patients with WNT tumors were grouped into 3 strata: W1 (M0, R0, classic histology, monosomy of chromosome 6); W2 (M0, R0, without monosomy 6 or classic histology); W3 metastatic (M+), residual disease (R+), or MYC/MYCN amplification. Treatment of W1 consisted of 15-Gy CSI/51-Gy primary site (0.5cm CTV margin) followed by 4 cycles of chemotherapy resulting in cumulative doses of 8 mg/m2 vincristine, 300 mg/m2 cisplatin, 12 gm/m2 cyclophosphamide. Serial audiology, neurocognitive, and endocrine evaluations were conducted over a six-year follow-up period. RESULTS From 2013-2022, 72 patients enrolled onto the W1 stratum: median age was 10.3 years (4.9-22.0); 62.5% female; median time of follow-up was 4.5 years (1.1-10.1). 5-year progression-free survival (PFS) and overall survival were 90.4 ± 5.1% and 98.6 ± 2.1%, respectively. Five patients had PFS events: 4 relapses and 1 accidental death. Relapsed disease was local in 2, distant in 1, and mixed in 1. Time to relapse was 2 years from enrollment for 3 patients. Severe ototoxicity (SIOP grade ≥ 3) at the end of therapy occurred in 14.4 ± 4.5%. Neurocognitive, endocrine, and detailed molecular data are forthcoming. CONCLUSIONS Patients with low-risk WNT-MB maintained a high PFS (90%) when treated with reduced-dose CSI and reduced-dose cyclophosphamide-based chemotherapy. Preliminary data suggests fewer treatment-related side effects.