BackgroundThe roles of γδ T cells in patients with breast cancer (BC) have not been fully clarified, although the efficacy of gamma delta (γδ) T cells, which combine both innate and adaptive potential have extraordinary properties, such as recognizing tumor cells without the need for major histocompatibility complex (MHC) antigen presentation, as well as killing a broad range of tumor cells through their strong cytotoxic and pro-inflammatory activity, has been suggested in the majority of patients with some certain cancers. PurposeTo understand and dissect the association between γδ T cells and the clinical pathology of BC by measuring and analyzing the γδ T cell populations in the patients with BC. MethodsOn the one hand, γδ T cells were measured and analyzed by extracting from peripheral blood mononuclear cells (PBMC) of patients with BC. On the other hand, γδ T cells were measured and analyzed by performing enzymatic digestion in primary BC tissues, cancer adjacent tissues, and distant normal breast tissues from patients with different stages of cancer progression. In addition, patients with breast benign tumors and healthy volunteers were also collected as controls for this study. ResultsThe proportion of γδ T cells in PBMC was significantly correlated with tumor histological grade, ER status, the proportional value of Ki-67, and lymph node (LN) metastasis. The decrease and exhaustion of γδ T cells were a general feature in the PBMC of BC patients. In addition, the primary BC tissue infiltration of γδ T cells was significantly associated with tumor histological grade, ER status, the proportional value of Ki-67, and LN metastasis. ConclusionThese findings suggest that γδ T cell populations are crucial for understanding the clinicopathological features of patients with BC, and may serve as a valuable and independent biomarker, as well as a potential therapeutic target for human BC.