ERBB2 and cancer: Using different molar ratios (1:2, 1:4, 1:6,1:8) to conjugate Trastuzumab-Streptavidin and biotinylated-Saporin, we showed decreased binding to Her2-expressing cancer cells and reduced cancer cell viability with higher molar ratios of Trastuzumab-SB-Saporin conjugation.