To investigate the ability of aptamers to traverse through an endothelial monolayer and to retain functionality and specifically target EpCAM-positive cancer cells, MDA-MB-231 cells were seeded in the abluminal compartment of the in vitro BBB model alongside cells devoid of EpCAM expression (HEK293T) at a ratio of 1:1. The gene discussed is EPCAM; the disease is cancer.