MKI67 and neoplasm: We found an increase, although not significant, in Ki67+ cells content of PDOs from tumor #1 and #6 (PF ependymoma Group A, Fig 3D′ and D′′′), while this increase was statistically significant in PDOs from tumor #21, tumor #22 (pilocytic astrocytomas) and tumor #23 (polymorphous low‐grade neuroepithelial tumor of the young—PLNTY) compared to the parental tumor, most likely due to the culture conditions (Fig 3F).