Metformin will be useful in suppressing cell proliferation and inducing apoptosis in cancer cells and CSCs that express OCTs, which support the intracellular accumulation of metformin, while, cancer cells, and CSCs that overexpress metformin extrusion transporters (MATE1 and PMAT) will confer resistance to metformin treatment [71,72,73,74]. The gene discussed is SLC47A1; the disease is cancer.