Moreover, in breast cancer brain metastasis, a bifunctional aptamer with non-covalently intercalated DOX and targeting TfR and EpCAM passes through the BBB by transcytosis and is specifically and selectively internalized into tumor cells, where it delivers DOX in a pH-dependent manner; it also enables a greater tumoral uptake and retention of DOX than free drug administration [81,104]. The gene discussed is TFRC; the disease is neoplasm.