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 aberra- tions), 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 re- sidual 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: me- dian 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 enroll- ment 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 sug- gests fewer treatment-related side effects.