To further investigate the role of TNFRSF9 in breast cancer, we knocked down TNFRSF9 through transfecting MCF-7 cells and ZR-75-30 with si-TNFRSF9, as these two cell lines have the lowest TNFRSF9 expression in all the breast cancer cell lines. Here, TNFRSF9 is linked to breast cancer.