ER+ tumors are characterized by changes in the stromal compartment, with enrichment of endothelial cells (endo ACKR1, CXCL12, RGS5) and depletion of cancer-associated fibroblasts (iCAFs2 and myCAFs4), inflammatory monocytes (Mon S100A9), and B naive cells, compared with TNBC (Fig. 3B). Here, S100A9 is linked to cancer.