Moreover, the expression of miR-155 was tightly associated with the presence of mutants of p53, since the induced expression of either p53R248Q or p53R282W in the p53-null H1299 cells was associated with a dose-dependent increased expression of mature miR-155 levels while knockdown of endogenous mutant p53 in BT-549 (p53R249S) down-regulated miR-155, suggesting that miR-155 is a mutant p53 target in breast cancer cells. This evidence concerns the gene TP53 and breast cancer.