Expression of the CXCL9 protein in tissue specimens from patients with invasive breast cancer. (a) Representative immunohistochemical staining with the monoclonal antibody to CXCL9 showing staining predominantly in the cytoplasm of tumor cells and in the extracellular matrix. (b) No immunoreactivity was seen using isotype matched controls. Different breast cancers showed (c) strong, (d) weak, or (e) no CXCL9 expression. Besides expression in cancer cells and the extracellular matrix, CXCL9 was also found in endothelial cells (arrows in f). Nuclei were counterstained with hematoxylin. Bars in c to e, 200 μm.