Background <p>Among the various types of breast cancer that endanger women’s lives, triple-negative breast cancer (TNBC) stands out due to its extreme heterogeneity, aggressive nature, and high likelihood of recurrence. The absence of unique targets and targeted drugs is a major factor contributing to the failure of cancer treatments and the eventual death of patients.</p> Methods <p>Single-cell RNA sequencing (scRNA-seq) was applied to investigate the immune microenvironment of TNBC, facilitating the detection of key cell subpopulations and regulatory genes. The mRNA expression of SLC31A1 in macrophages was measured by qPCR. Flow cytometry was utilized to ascertain the M2 macrophage proportion and cancer cell apoptosis. Transwell and scratch assays were conducted to gauge cancer cell migration and invasion. Copper ion and H₂O₂ detection kits were employed to evaluate the copper ion content and oxidative stress levels in macrophages.</p> Results <p>SLC31A1 overexpression in TNBC myeloid cells, particularly macrophage subpopulations, was identified through scRNA-seq analysis. Cluster and pseudotime analyses showed that macrophages with high SLC31A1 expression are often in advanced stages of cell growth, accompanied by notable changes in oxidative stress. Functional studies revealed that knocking down SLC31A1 in macrophages significantly reduced M2-type polarization. The conditioned medium from these macrophages markedly inhibited TNBC cell migration and invasion, while promoting apoptosis. Furthermore, SLC31A1 knockdown resulted in decreased copper ion content and H₂O₂ levels in macrophages.</p> Conclusion <p>SLC31A1 enhances the malignant phenotype of TNBC cells by inducing M2 polarization in macrophages.</p>