Currently, the relationship between the trinucleotide repeat containing 9 (TNRC9) rs3803662 C>T polymorphism and risk of breast cancer (BC) is uncertain. Here, we attempted to obtain a more accurate assessment of this association by conducting a meta-analysis of all eligible case-control investigations, comprising 44,820 cases and 58,316 controls. A comprehensive search was performed to identify all suitable studies involving the TNRC9 rs3803662 polymorphism and BC risk. Pooled odds ratios (ORs) and 95% confidence intervals (95%CIs) were estimated using fixed- or random-effect models. Heterogeneity, publication bias, and sensitivity analyses were also carried out. We found that the variant T allele of rs3803662 C>T greatly increases BC risk (CT vs CC: OR = 1.14, 95%CI = 1.07-1.22, P < 0.001; TT vs CC: OR = 1.38, 95%CI = 1.25-1.53, P < 0.001; CT/TT vs CC: OR = 1.19, 95%CI = 1.11-1.28, P < 0.001; TT vs
Ct/cc: OR = 1.28, 95%CI = 1.19-1.38, P < 0.001). Stratified analysis based on ethnicity also revealed a markedly increased risk in Asian and Caucasian populations. Moreover, studies with hospital-based control groups showed elevated risk under the four genetic models employed, as did those using population-based controls, except under heterozygote comparison. The TNRC9 rs3803662 C>T polymorphism is greatly related to increased risk of BC, in both Asian and Caucasian populations.