In order to clarify how metformin affects the pathogenesis and pathological progression of CRC with type 2 DM, we examined the associations of metformin with the pathological type and the incidence of metastasis of CRC in diabetic patients complicated with CRC and the antiproliferative effect of metformin on colorectal CSCs (CD133+) as well. The gene discussed is PROM1; the disease is colorectal carcinoma.