In a mouse breast cancer model, tumor-induced transforming growth factor beta (TGF-β) induced CD8 T cells to produce IL-17. In vitro, IL-17 in turn suppressed apoptosis of 4T1 mouse mammary carcinoma, CT26 mouse colon carcinoma, and MDA-MB231 human breast carcinoma cell lines. This evidence concerns the gene IL17A and breast cancer.