Analysis of cell-cycle checkpoint inhibitors revealed that Nf1–/– DNp53 male astrocytes have greater time-dependent phosphorylation of retinoblastoma protein (RB), which is a tumor suppressor, resulting in a greater level of E2F-dependent transcription and less cell cycle regulation when compared to Nf1–/– DNp53 female astrocytes (25, 29). This evidence concerns the gene RB1 and neoplasm.