A new single-cell RNA-sequencing dataset provides in-depth profiling of estrogen receptor (ER)-positive primary and metastatic breast cancer tumors from 23 patients, offering insight into the biological changes associated with metastatic progression. By characterizing tumors at single-cell resolution, the study delineates shifts in the tumor microenvironment, including enrichment of immunosuppressive cell populations in metastatic lesions such as CCL2+ macrophages, exhausted cytotoxic T cells, and FOXP3+ regulatory T cells. The analysis also reveals reduced tumor–immune cell communication in metastases, alongside increased TNF-α/NF-κB signaling activity in primary tumors, highlighting potential therapeutic targets. This comprehensive resource advances understanding of the cellular and molecular dynamics that shape breast cancer progression and metastasis.
