The observed cellular uptake clearances (OATP1A2 > OCT1 > OCT3 > OCT2) along with gene expression data in breast cancer (OCT3 > OCT1 > OATP1A2; OCT2 not expressed) and cardiac tissue (OCT3 > OCT1; OCT2 and OATP1A2 not expressed) point to an outstanding role of OCT3 in both efficacy and safety. The gene discussed is POU2F1; the disease is breast cancer.