SMARCB1 and rhabdoid tumor: Mutations in the ATRX gene result in a loss of nuclear protein expression in tumor cells, but retained expression in non-tumor cells (e.g., endothelial cells, pre-existing glial cells), which serve as a positive internal control (Figure 1B), analogously to the expression of INI1/SMARCB1 protein in atypical teratoid/rhabdoid tumors.