We evaluated the potential effects of ATO in different pediatric SHH-MB cell lines (ONS-76: TP53wild type; DAOY and UW402: TP53-mutated). MB cell lines molecular subgroup was confirmed and TP53 mutations were validated. Cell viability, clonogenicity and apoptosis were evaluated after ATO treatment at different concentrations (1-16 µM) alone or combined with irradiation doses (0.5, 1, 2 and 4 Gy). Rad51 and Ku86 proteins were evaluated by WB. ATO treatment reduced cell viability for all SHH-MB cell lines. Significant decrease of clonogenic capacity and higher apoptosis rates were also observed after ATO exposure, being cell death more pronounced (>70%) for the SHH-MB TP53mutated. Combined treatment of ATO with irradiation also reduced colonies formation in UW402 tumor cells, which was independent of DNA damage repair proteins Rad51 and Ku86. In silico analyses suggested that a set of genes from cell cycle and p53 pathways are differentially expressed in SHH tumor subtypes, suggesting that cell lines may respond to therapies according to the gene expression profiles. Herein, we showed ATO cytotoxicity in pediatric SHH cell lines, with marked radiosensitizing effect for the MB-SHH TP53-mutated cells. These results highlight the potential of ATO, alone or in combination with radiotherapy, supporting further clinical investigations. Medulloblastoma (MB) is the most common malignant brain tumor in children, corresponding to approximately 20% of all brain tumors in patients less than 15 years of age. MB is responsible for significant morbidity and mortality rates 1. Recently, twelve distinct subgroups allocated to four main molecular classes (SHH, WNT, Group 3 and Group 4) have been recognized for MB: WNT-alpha and beta; SHH-alpha, beta, gamma and delta; Group 3-alpha, beta and gamma; and Group 4-alpha, beta, and gamma 2. Considering the clinical significance of the MB molecular classification, new therapies that contemplate the genetic aspects of the disease are required 3. The majority of SHH-MB cases presents somatic mutation in one or more genes of the Sonic Hedgehog (SHH) pathway (i.e., PTCH1, SUFU, or SMO), contributing to its constitutive activation. SHH signaling is essential for embryonic development, as well as it can lead to a tumor arising when aberrantly activated 4. The SHH-MB subgroup prognosis in children is mostly favorable, but the clinical outcome varies within this subgroup. SHH-MB alpha cases are rarely observed in infants and carry the poorest prognosis, which is associated with MYCN and GLI (glioma-associated oncogene homolog) amplification, and higher TP53 mutational burden. In contrast, SHH-MB beta and gamma subtypes affect mainly infants, being one-third of the SHH-MB beta cases metastatic at presentation with frequent focal PTEN deletions. The SHH-MB gamma is strongly related to MB with extensive nodularity (MBEN) histology, in general, presents wild type TP53, and excellent prognosis 2. Lastly,