By analyzing the gene expression data of primary breast cancer samples of patients who developed brain metastasis (n = 13) or metastasis to organs other than the brain (n = 9), the expression levels of the IFN-γ-inducible chemokines CXCL9, -10, −11, and their receptor CXCR3, were found to be significantly higher in the primary breast cancers from patients who developed brain metastasis (Fig. 6a, b, c and e). The gene discussed is CXCL9; the disease is breast cancer.