The results of this retrospective analysis suggest that more research is indicated to investigate the hypothesis that presence or absence of FES-PET may be useful in discriminating between a hormonally active HER2-positive tumor that could respond to a non-chemotherapy treatment backbone, versus a tumor in which the HER2 pathway is dominant and thus less likely to respond to a chemotherapy-free, endocrine+/HER2-targeted approach. Here, ERBB2 is linked to neoplasm.