Stress Promotes Lung Metastasis in Breast Cancer by Altering Neutrophil Differentiation

Mental stress is widely recognized as a significant risk factor for breast cancer, exerting detrimental effects on both progression and prognosis. Herein, we investigated the role of stress in regulating breast cancer metastasis. In genetically engineered and transplantation breast cancer mouse models, chronic stress stimulation increased tumor growth and lung metastasis. Single-cell RNA-sequencing analysis of the pre-metastatic lung microenvironment revealed induction of a previously unrecognized subtype of cancer stress-primed (CSP) neutrophils, characterized by the overexpression of Ccl3, Ccl4, Cxcl2, Il1r2, and Cebpb. Pseudotime trajectory analysis demonstrated that chronic stress caused a shift of neutrophils from the cancer-primed (CP) neutrophil subtype to the CSP subtype in the lung. Activation of the glucocorticoid receptor NR3C1 by the stress hormone corticosterone induced expression of Cebpb in neutrophils, which then promoted transcription of Ccl3 and Ccl4. The differentiation of neutrophils into the CSP subtype promoted lung metastasis of CCR1+ breast cancer cells via CCL3/CCL4-mediated recruitment. Targeting this axis using an anti-Ly6G antibody to deplete neutrophils, a CRISPR/Cas9-mediated approach to conditionally knockout Ccl3/Ccl4 in neutrophils, and BX471 treatment to inhibit CCR1 in cancer cells all significantly reduced breast cancer lung metastasis. Together, this study not only demonstrates a stress-neutrophil-cancer axis that promotes lung metastasis in breast cancer but also provides potential strategies for reducing lung metastasis by targeting CSP neutrophils or CCR1+ breast cancer cells.