ITGAM and neoplasm: Here, our study of the in vivo synthetic MN model addresses the controversy about Gr1+CD11b+Ly6G+ neutrophils in breast cancer by revealing the pro-tumor roles of neutrophils in regulating lung-tropic metastatic dissemination of breast cancer cells and supporting metastatic outgrowth as well as their antitumor roles in boosting antitumor immunity and driving metastatic dormancy in some conditions.