MBCL-22. EFFICACY OF DOUBLE-CONDITIONING REGIMEN COMPRISING THIOTEPA AND MELPHALAN FOR RELAPSED MEDULLOBLASTOMA – A SINGLE INSTITUTION EXPERIENCE

Abstract BACKGROUND The prognosis of relapsed medulloblastoma was dismal. Recently, we published the promising outcome of metastatic medulloblastomas treated with a double-conditioning regimen comprising high-dose thiotepa and melphalan (HD-TM). Here, we report a single-center study of HD-TM for relapsed medulloblastomas. MATERIALS AND METHODS From April 2006 to January 2019, 17 consecutive medulloblastoma patients with the first relapse were identified, and of which 10 received HD-TM were retrospectively reviewed. RESULTS The median age at first relapse was 11.9 years (range 1.8–31.7). The median follow-up period was 23.5 months after 1st relapse. Four localized relapses at the posterior fossa and 6 metastatic relapses including 3 with multiple sites were observed. Surgical resection and re-irradiation were administered in 5 and 9 patients, respectively. Two-year PFS and OS after relapse were 21±18.1% and 60±21.9%, respectively, and significantly better than in patients who did not receive HD-TM. Among 7 evaluable patients, tumor shrinkage was observed in 6 after HD-TM administration including 3 patients who were resistant to prior chemotherapy. At the present time, 5 patients are alive with no evidence of disease (NED). The last 5 patients received re-irradiation including 12 Gy craniospinal irradiation (CSI), and 4 are alive with NED. In multivariate analysis for all patients, both HD-TM and re-irradiation were associated with improved OS and PFS, but disseminated relapse had no prognostic value (p=0.56). CONCLUSION HD-TM contributes to prolonged survival when combined with re-irradiation. HD-TM might become a curative approach for relapsed medulloblastoma, especially when combined with CSI.