p53 expression was often widespread in the severely anaplastic medulloblastoma, ATRT, and sPNET groups, with 6 of 12 tumors showing immunoreactivity in over 25% of cells, while classic and nodular medulloblastomas always had fewer than 25% immunopositive cells (Table 1). This evidence concerns the gene TP53 and atypical teratoid rhabdoid tumor.