Myeloid-derived suppressor cells are increased and correlated with type 2 immune responses, malnutrition, inflammation, and poor prognosis in patients with breast cancer.

Myeloid-derived suppressor cells (MDSCs) have been identified in the majority of patients and experimental mice with tumors by their suppression of T cell activation. MDSCs have also been reported to be associated with chronic inflammation. In advanced cancer, the T helper (Th) cell balance tends to shift from Th1 to Th2 predominance, and immune function, including cell-mediated immunity, is impaired by cytokines produced by Th2 cells. The present study examined the correlations between MDSC levels and inflammation, immune suppression, malnutrition, and poor prognosis in 155 patients with breast cancer. The levels of MDSCs in preoperative patients and in patients with recurrent breast cancer were significantly higher compared with postoperative patients, patients with recurrent breast cancer who received chemotherapy and healthy volunteers. The MDSC levels of preoperative patients were significantly positively correlated with interleukin (IL)-6 production by peripheral blood mononuclear cells (PBMCs), the neutrophil/lymphocyte ratio and C-reactive protein, and were negatively correlated with the production of interferon-γ and IL-12, serum concentration of rapid turnover protein, and the stimulation index. These patients were divided into two groups based on the levels of MDSCs. In preoperative patients with MDSC levels >1.0% of total PBMCs, the overall survival of patients with stage IV disease was significantly shorter compared with other disease stages, and was also significantly shorter compared with patients with MDSC levels <1.0% of total PBMCs. Thus, the MDSC levels of preoperative patients may function as a good prognostic indicator, particularly in patients with advanced breast cancer.