Increased levels of stromal TGF‐β and SDF‐1 staining are also reported to be associated with the poor outcomes in breast cancer patients.46, 47 Although these cytokines are highly produced by CAFs, as indicated earlier, it remains unclear whether CAF‐derived TGF‐β and SDF‐1 in tumors contribute to poor prognoses via downregulated stromal CD26 expression in breast cancer patients. This evidence concerns the gene CXCL12 and breast cancer.