A statistically significant increase in p53 immunopositivity in AT/RT and sPNET Most classic and nodular medulloblastoma (MB) contained no p53 immunopositive cells. In contrast, p53 positive cells were present in many anaplastic MB, supratentorial primitive neuroectodermal tumors (sPNET) and atypical teratoid rhabdoid tumors (ATRT). Triangles represent individual tumors with negative (0), weak (1) or strong (2) p53 immunostaining. Bars represent the mean and standard error of the mean. The increase in p53 immunopositivity in the sPNET/ATRT category as compared to classical MB was statistically significant (Mann Whitney test).