Flow cytometry analysis demonstrated that, in contrast to the normal cell line (HEK-293) or the EphA2-low-expressing cell line (MCF-7), the immunotoxin could bind significantly (approximately 99%) to the EphA2-overexpressing breast cancer cell line (MDA-MB-231) at a low concentration (2.5 ng/μL). This evidence concerns the gene EPHA2 and breast cancer.