Text Box: CLINICAL SIGNIFICANCE AND RELATIONSHIP BETWEEN CENTRAL NERVOUS SYSTEM LEUKEMIA AND MINIMAL RESIDUAL DISEASE IN ACUTE LYMPHOBLASTIC LEUKEMIA XIA Yan, LI Wenyi, Guo Haixia, Den Qingli, Fang Jianpei, Xue Hongmang, Zhou Dunhua Sun Yat-Sen Memorial Hospital, Sun Yat-Sen University of Medical Sciences, GuangZhou, China Objective: To explore clinical significance and analyze the level or changes of minimal residual disease (MRD) correlated with central nervous system leukemia relapse (CNLS) in acute lymphoblastic leukemia (ALL). Methods: A improved one-step boiling to extract DNA procedure and nested-PCR were applied in this study while TCRγ,IgH,TCRδwere used as markers, Kaplan-Meier method and COX model were used to analysis of the data . Results: Among 46 cases of ALL, the level of MRD in marrow by the time of complete remission (CR) positive correlated with CNLS (γ=0.3496，P<0.05) and detected MRD in cerebrospinal fluid (CSF) by the time of CR also positive correlated with CNLS (P<0.05). During the period of CR, the cases whose MRD in CSF were persistently positive or form negative to positive, had high possibility at risk for CNLS (P<0.05). Conclusion: Minimal residual disease by the time of CR is a powerful prognostic factor in ALL, detection of MRD by PCR should be used to identify patients at risk for CNLS and dynamic monitoring MRD in cerebrospinal fluid could be valuable in guiding the management of ALL and predicting CNSL. 【Key words】 acute lymphoblastic leukemia; minimal residual disease; CNLS 2320