NCR1 and metastatic neoplasm: To identify which immune cell type(s) in the tumor environment were affected by nicotine and contributed to differential outgrowth of primary and metastatic tumors, we examined the composition of neutrophil (ELA2), macrophage (F4/80), and NK (NKp46) cells in primary and metastatic tumors of control and nicotine-treated mice by immunohistochemical (IHC) analysis (Fig. 1G, Supplementary Figs. 1G and 2E).