Null polymorphism of GSTM1 gene in susceptibility of Breast Cancer: Evidence based on Meta-analysis Daiane O. Cunha, Paula Lailla F. Ribeiro, Xisto S. Passos, Cesar Augusto S. Tiago Vilanova-Costa, Hellen S. Cintra de Paula, Jacqueline Andréia B. Leão Cordeiro, Vera A. Saddi, Antonio Márcio T. Cordeiro Silva. Universidade Paulista (UNIP) – Campus Flamboyant, Goiânia, Goiás. Objective: To evaluate whether individuals with the GSTM1-null gene polymorphism have increased susceptibility to breast cancer. Methods: It was conducted a meta-analysis of 10 case-control studies with histological confirmed breast cancer that used PCR and/or DNA sequencing to determine the null polymorphism of GSTM1 gene. The analysis was performed after collecting the necessary data from the evaluated studies (author, publication year and study site). Statistical calculations and the data representation were set with the BioEstat® 5.0 software. Results: After grouping the data of the studies, the total number of individuals evaluated was 7,607 (3,759 cases and 3,848 controls). The frequencies for the null polymorphism of GSTM1 gene were, respectively, 51.0 % in the case group and 50.3 % in the control group. The data obtained by the meta-analysis were: OR = 0.967 and CI (95%) = 0.883 to 1.060. Conclusion: According to the results of this meta-analysis, it was not found any association between GSTM1-null polymorphism and the development of breast cancer. Those data show that the polymorphism in question is not involved in the susceptibility to breast cancer, thus, other factors, such as smoking status, other genetic polymorphisms and parity should be considered. Keywords: Breast cancer, polymorphism, GSTM1-null, susceptibility.