RESUMEN
BACKGROUND AND AIM: Gastrointestinal (GI) cancers are a heterogeneous group of cancers originating from the digestive system. Considering key roles of myeloid-derived suppressor cells (MDSCs) in the immunosuppression network, levels of MDSCs in patients with cancer are assumed to be of prognostic and predictive value. In this systematic review, we aimed to evaluate the clinical relevancy of MDSCs and their relationship with clinical features and prognosis of GI malignancies in patients with GI cancers. METHODS: We searched Medline, Scopus, DART, OpenGrey, and ProQuest without applying any language filter up to 1 August 2015. Two of the authors independently reviewed search results for irrelevant and duplicate studies and extracted data from studies. We used tabulation to synthesize the findings of the studies and transformed data into a common rubric and calculated a weighted treatment effect across studies using Review Manager. RESULTS: We found 1238 references in five databases, and after exclusion of irrelevant and duplicate studies, 17 studies with a total number of 1115 patients with GI cancers were included. A meta-analysis of three studies showed associations of high MDSC levels with higher mortality during follow-up periods (hazard ratio = 3.35; 95% confidence interval = 1.46-7.68, P = 0.0004). A meta-analysis of four studies showed that patients with higher levels of MDSC had higher odds of having an advanced cancer (odds ratio = 2.64; 95% confidence interval = 1.53-4.53; P = 0.0004). There were also significant associations between MDSC levels and relapse, tumor progression, lymph node involvement, and metastasis. CONCLUSION: In conclusion, results of this systematic review based on the available literature suggest that MDSC levels are of clinical relevancy and prognostic and predictive value.