It was demonstrated that human tumors are complex and non-uniform in terms of expression of many tumor markers106 and individual cancer cells can strongly differ even in p53 expression.107 Studying the effects of miR-34a in models with disrupted p53 function can therefore help to predict possible effects in tumor cells harboring defective p53, especially regarding the feedback regulation between miR-34a and p53 (Figure 1). This evidence concerns the gene TP53 and cancer.