ESR2 and cancer: On the basis of its fully human nature and selectivity of its antitumour action on target cells, Erb-hcAb-RNase represents a promising valuable tool in cancer therapy, thus supporting the hypothesis that the scFv-Fc-RNase format is the most appropriate for the production of a novel generation of IR better suited for therapeutic applications, as it combines the advantages of the first generation IR with those of functional relevant antibody domains.