ERBB4 and neoplasm: Nevertheless, the molecular signalling background responsible for the higher efficiency of HerceptinTM treatment in HER2-positive/HER4-positive patients versus HER2-positive/HER4-negative patients needs to be experimentally elucidated in detail and the experimental design should allow for investigating the predictive relevance of HER4 in consideration of its oncogenic and tumour suppressing potential, respectively.