According to this study, we propose a possible mechanism by which a highlevel of ER reduces Th17 cell infiltration in tumor tissues, thereby decreasing the levels of IL-17A and IL-17F, weakening the intensity of IL-17A and IL-17F signal transduction, and finally downregulating the expression level of PD-1/PD-1 and the infiltration level of CD8+ T cells in breast cancer. The gene discussed is PDCD1; the disease is breast carcinoma.