Macrophages are pivotal in driving breast tumor development, progression, and resistance to treatment, particularly in estrogen receptor-positive (ER+) tumors, where they infiltrate the tumor microenvironment (TME) influenced by cancer cell-secreted factors. By analyzing single-cell RNA sequencing data from 25 ER+ tumors, we elucidated interactions between cancer cells and macrophages, correlating macrophage density with epithelial cancer cell density. We identified that S100A11, a previously unexplored factor in macrophage-cancer crosstalk, predicts high macrophage density and poor outcomes in ER+ tumors. We found that recombinant S100A11 enhances macrophage infiltration and migration in a dose-dependent manner. Additionally, in a 3D matrix using a panel of three ER+ breast cancer cell lines, we showed that secreted S100A11 levels from cancer cells were associated with increased monocyte infiltration that subsequently differentiation toward macrophages. Genetic silencing of S100A11 in the S100A11-high T47D cancer cells reduced monocyte infiltration, consistent with results using a S100A11 blocking antibody in T47D cancer cells and in a clinically relevant patient-derived organoid model. Phenotypic analysis of macrophages cocultured with T47D cancer cells following S100A11 knockdown revealed lower expression of the immunosuppressive marker CD206, further underscoring the role of S100A11 as a paracrine regulator of pro-tumorigenic cancer-macrophage crosstalk. This study offers novel insights into the interplay between macrophages and cancer cells in ER+ breast tumors, highlighting S100A11 as a potential therapeutic target to modulate the macrophage-rich tumor microenvironment.

Cancer-cell derived S100A11 promotes macrophage recruitment in ER+ breast cancer