In 82.3 cells, we observed overexpression of HIF1A; in medulloblastoma, the upregulation of HIF1A correlated with a worse response to cyclophosphamide through the inhibition of a gene of the cytochrome p450 family, CYP3A5 [25], also found to be down-regulated in our model. The gene discussed is HIF1A; the disease is medulloblastoma.