In an effort to optimise the targeting and therapeutic efficacy of ALM, we hypothesise that strategies to alter the affinity for either one or both of the arms for their target antigens can be used to increase the window of selective targeting achievable with bs-scFvs targeting ErbB2‘+’/ErbB3‘+’ tumours although not impairing the overall tumour retention. This evidence concerns the gene ERBB3 and neoplasm.