SLC22A3 and breast cancer: who compared metformin uptake levels and inhibiting activity on cancer cell growth in a human breast cancer cell line (BT-20) deficient in OCTs and a BT-20 cell line overexpressing organic cation transporter 3 (OCT3), OCT3-BH20 cells: OCT3 is also a predominant transporter in human breast neoplasms (241).