Abstract:Objective To systematically evaluate the associations of the expression level of long non-coding RNA cancer susceptibility candidate 9 （CASC9） with the clinical characteristics and prognosis of cancer patients. Methods The databases of PubMed, Web of Science, The Cochrane Library, Embase, OVID, WanFang Data, VIP and CNKI were searched to collect the case-control studies on the correlations between CASC9 expression and the prognosis of patients with malignant tumors. The retrieval time limit was from the establishment of the databases to May 30, 2021. Results A total of 20 case-control studies (including esophageal cancer, oral cancer, gastric cancer, etc.) involved 2560 patients with malignant tumors. Meta-analysis showed that the high expression of CASC9 was significantly associated with age（OR=1.35, 95%CI:1.07-1.71）, tumor size（OR=1.58, 95%CI:1.19-2.11）, lymph node metastasis（OR=3.76, 95%CI:2.70-5.23）, T staging（OR=2.78, 95%CI:1.77-4.36）,clinical staging（OR=3.08, 95%CI:2.37-4.01）, overall survival（HR=1.65, 95%CI:1.47-1.85），but wasn't correlated with gender（OR=0.97,95%CI:0.75-1.25）and degree of tumor differentiation（OR=1.41,95%CI:0.97-2.05）. Conclusion The high expression of CASC9 may be a risk factor for poor prognosis of patients with malignant tumors. CASC9 can be used as a potential biomarker to evaluate its prognosis.