TP53 and neoplasm: Importantly, the GD2high derivatives of C4-2 exhibited significantly elevated 3D tumor-sphere growth, an in vitro correlate of CSC activity40, with RB1-KD yielding ~ 4.5-fold and TP53-KD or DKD cell lines yielding ~ ninefold more tumorspheres (p-values < 0.001) compared to their GD2low parental C4-2 cells (Fig. 3C, upper panel).