As mentioned above, previous studies have shown that metformin treatment results in an increase in let-7 levels in breast cancer-derived MCF-7 cells.12 Here we confirmed and extended these results by demonstrating that metformin (or AICAR) treatment leads to an increase in let-7 (Figure 4a), a decrease in H19 (Figure 4b) and an increase in SAHH activity (Figure 4c) in MCF-7 cells. This evidence concerns the gene AHCY and breast carcinoma.