CXCR2 and neoplasm: In contrast to <i>wild-type</i> (<i>WT</i>), <i>Fpr1</i><sup>-/-</sup>, and <i>Fpr2</i><sup>-/-</sup> mice, neutrophils were almost completely absent in 4T1 tumors from <i>Cxcr2</i><sup>-/-</sup> mice, indicating a dominant role for CXCR2 in the recruitment of tumor-associated neutrophils, leading us to use <i>Cxcr2</i><sup>-/-</sup> mice for further studies.