By analyzing mRNA expression in MDA-MB-231 breast cancer cells and in monocytes (THP-1 or U937), respectively, after co-culturing for 48 h, CXCL7 levels were found to be strongly enhanced in the THP-1 or U937 monocytes co-cultured with MDA-MB-231 cells (Fig. 1B, C), and the same phenomenon was observed upon co-culturing of the monocytes with another breast cancer cell line, Hs578T cells (Fig. S1C). This evidence concerns the gene PPBP and breast cancer.