TP53 and neoplasm: The observed lack of Trp53 mutations in the Brm-negative phenotype was not likely due to loss of Trp53 expression via p19Arf1 mutations or Mdm2 amplifications, since Trp53 was expressed in the vast of majority of tumor cells (>85%) by IHC and was not qualitatively different between Brm-negative tumors and Brm-positive tumors (Supplementary Figure 1).