INTRODUCTION
Intensive treatment including high-dose chemotherapy (HDC) with autologous stem cell transplantation (SCT) is the standard care for high-risk neuroblastoma.1 The importance of HDC is well recognized, even after improvement of treatment outcomes by anti-GD2 antibody immunotherapy, so re-evaluation of the efficacy and safety of the HDC regimen is ongoing in several clinical trials.2 Recently, the International Society of Paediatric Oncology European Neuroblastoma (SIOPEN) conducted a randomized trial and proved the superiority of busulfan and melphalan over melphalan, etoposide, and carboplatin as a conditioning HDC regimen.3
Thiotepa is an alkylating anticancer agent broadly used in the HDC regimen at various dosages and schedules including both single4 and tandem settings5–7. In Japan, a unique HDC regimen called the double-conditioning regimen is widely used in some major pediatric cancer centers, in which thiotepa and melphalan are administered for 2 consecutive weeks. Hara et al. (1998) reported the feasibility and efficacy of the double-conditioning regimen for various solid tumors, including neuroblastoma.8 Okada et al. (2019) reported toxicity profiles of the double-conditioning regimen in a further cohort.9 Recently, high efficacy of the double-conditioning regimen for high-risk medulloblastoma was published.10 In contrast, few studies have investigated the double-conditioning regimen for high-risk neuroblastoma.11 This study re-evaluated the safety of the double-conditioning regimen and assesses its efficacy for high-risk neuroblastoma in a multi-institutional cohort.