Considering that p53 levels were increased, that CDK2 and CDK4 levels were decreased at the protein level (Table 1), and that p21 levels were unchanged, we suggest that the enhanced p53 expression seen in si-hVDAC1- treated residual tumours is associated with cell differentiation, whether by cells expressing native ( i.e., U-87MG and A549 cells) or mutated p53 (i.e., MDA-MB-231 cells), via mechanisms independent of cell death [31]. This evidence concerns the gene CDK4 and neoplasm.