Namely, the anti-diabetic drug metformin (150 mg/kg/day; p.o.)was found to suppress melanoma (evoked by subcutaneous injection of B16-F10 cells) progression in non-diabetic C57BL/6 mice as well as in diabetic KK-Ay mice by inhibiting the lysine acetyltransferase 5 (KAT5)/TRIB3/SMAD3 positive feedback loop. The gene discussed is TRIB3; the disease is melanoma.