Pancreatic cancer has the highest mortality rate of all major cancers, with a 5-year survival rate of about 10%. Early warning signs and symptoms of pancreatic cancer are vague or nonexistent, and most patients are diagnosed in Stage IV, when surgery is not an option for about 80%–85% of patients. For patients with inoperable pancreatic cancer, current conventional treatment modalities such as chemotherapy and radiotherapy (RT) have suboptimal efficacy. Tumor progression is closely associated with the tumor microenvironment, which includes peripheral blood vessels, bone marrow-derived inflammatory cells, fibroblasts, immune cells, signaling molecules, and extracellular matrix. Tumor cells affect the microenvironment by releasing extracellular signaling molecules, inducing peripheral immune tolerance, and promoting tumor angiogenesis. In turn, the immune cells of the tumor affect the survival and proliferation of cancer cells. Myeloid-derived suppressor cells are key cellular components in the tumor microenvironment and exert immunosuppressive functions by producing cytokines, recognizing other immune cells, and promoting tumor growth and metastasis. Myeloid-derived suppressor cells are the main regulator of the tumor immune response and a key target for tumor treatments. Since the combination of RT and immunotherapy is the main strategy for the treatment of pancreatic cancer, it is very important to understand the immune mechanisms which lead to MDSCs generation and the failure of current therapies in order to develop new target-based therapies. This review summarizes the research advances on the role of Myeloid-derived suppressor cells in the progression of pancreatic cancer and its treatment application in recent years.

Objective. Immunotherapy has shown better efficacy and less toxicity than chemotherapy in the treatment of non-small-cell lung cancer (NSCLC) at advanced stage. This study evaluates the safety and efficacy of neoadjuvant immunotherapy for resectable NSCLC. Methods. Literature examination was performed by searching the PubMed, the Cochrane Library, and Embase for articles evaluating the efficacy and safety of neoadjuvant immunotherapy for resectable NSCLC. The 95% confidence interval (CI) and effect sizes (ES) were evaluated. Heterogeneity and subgroup analysis were performed. Meta-analysis was carried out using Stata BE17 software. Results. In total, 678 patients from eighteen studies were recruited in this meta-analysis. The pathological complete response (pCR) and major pathological response (MPR) were used to evaluate the efficacy of neoadjuvant immunotherapy. Significantly higher MPR values were observed in neoadjuvant immunotherapy (MPR : ES = 0.44; 95% CI: 0.33–0.55; pCR : ES = 0.22; 95% CI: 0.15–0.30) compared with neoadjuvant chemotherapy (MPR < 25% and PCR : ES = 2%–15%). Treatment-related adverse events (TRAE), surgical resection rate, surgical delay rate, and incidence of surgical complications were used to evaluate the safety. In summary, ES values for the incidence of TRAE, incidence of surgical complications, and surgical delay rate were 0.4, 0.24, and 0.04, respectively, that were significantly lower than those for neoadjuvant chemotherapy (95% CI: 0.04–0.90; 0.22–0.75; and 0.01–0.10, respectively). The mean surgical resection rate of 89% was similar to the reported 75%–90% resection rate with neoadjuvant chemotherapy (OR = 7.61, 95% CI: 4.90–11.81). Conclusion. Neoadjuvant immunotherapy is safe and effective for resectable NSCLC.