ESR2 and cancer: As shown in Figure 2, both Erb-hRNase and Erb-hcAb caused a dose-dependent inhibition of colony formation in all cancer cells tested, proving to be effective also in trastuzumab-resistant JIMT-1 and KPL-4 cells, with an IC50 (concentration producing an inhibition of 50%) value of ∼50 and 100 nM, respectively.