Abstract: Objective To evaluate the prognostic value of histone deacetylase 9（HDAC9） expression in malignant tumor.Methods Databases including PubMed，EMbase，The Cochrane Library，CNKI and WanFang Data were searched to collect case-control studies about the prognostic value of HDAC9 expression in malignant tumor from inception to Jan 2019.Literatures were screened and data was extracted.Then meta-analysis was performed by using RevMan 5.3 software.Results Finally，a total of 8 case-control studies were included.The results of meta-analysis showed that the high expression of HDAC9 was not associated with gender（OR=0.87，95％CI =0.22～3.40，P=0.84），TNM staging（OR=0.55，95％CI =0.20～1.52，P=0.25）and progressionfree survival（HR = 1.10，95％CI =0.97～1.26，P=0.14）.But the high expression of HDAC9 was significantly associated with lymph node metastasis（OR=2.25，95％CI =1.18～4.29，P=0.01），overall survival（HR=2.51，95％CI =1.11～5.66，P=0.03）and eventfree survival（HR=10.61，95％CI =1.26～86.90，P=0.03）.Conclusion HDAC9 high expression is a risk factor for poor prognosis in cancer patients and may be used as a predictive maker for poor prognosis in malignant tumor.

Key words: histone deacetylase 9（HDAC9）, tumor, prognosis, Meta-analysis