ERBB2 and neoplasm: The lower levels of circulating neutrophils in patients who benefit from trastuzumab indicate the recruitment of these cells into the tumour microenvironment, where they likely participate in trastuzumab activity through their ability to mediate ADCC, as demonstrated in HER2-positive xenograft models.26 However, levels of circulating neutrophils may also inform about the activation status of patient immune system.