To directly study the role of Endo II in human HER2+ breast cancer cell lines, we first profiled Endo II expression in two HER2+ cell lines (SK-BR-3, HCC1954) alongside lines representing TNBC and luminal subtypes (MDA-MB-231 and BT-474, respectively), and a normal-like breast epithelial cell line (MCF-10A). This evidence concerns the gene ERBB2 and breast cancer.