ERBB2 and breast cancer: TetraFHER2 did not affect the viability of tested cells, whereasthe TetraFHER2-vcMMAE conjugate induced the appearanceof multiple propidium iodide signals only in HER2+ SKBR-3 breast cellsand was fully neutral to MCF-7 breast cancer cells that are devoidof detectable HER2 expression (Figure ).