Taken together, our study results not only demonstrate that chronic psychological stress promotes breast cancer progression via activating TAM/CXCL1 signaling in a GC/GR-dependent manner, but also highlight the role of CXCL1-CXCR2 signaling in mobilizing spleen MDSCs into the lung to establish PMN, thereby facilitating metastasis. Here, CXCR2 is linked to breast cancer.