Endogenous noncoding circular RNAs (circRNAs) have gained attention for their 
involvement in carcinogenesis, but their expression pattern in breast cancer has 
remained largely unknown. In this two-stage study, we first used an Arraystar 
Human circRNA Array to construct a genome-wide circRNA profile. We then selected 
candidate circRNAs for validation using a quantitative real-time polymerase 
chain reaction system. CircRNA/miRNA interactions were predicted and sequence 
analyses were performed. Among 1155 differentially expressed circRNAs, 715 were 
upregulated and 440 were downregulated in breast cancer tissues. The validation 
study demonstrated that hsa_circ_103110, hsa_circ_104689 and hsa_circ_104821 
levels were elevated in breast cancer tissues, whereas hsa_circ_006054, 
hsa_circ_100219 and hsa_circ_406697 were downregulated. These circRNAs targeted 
complementary miRNA response elements. The area under the receiver operating 
characteristic curve for distinguishing breast cancer was 0.82 (95% CI: 
0.73-0.90) when hsa_circ_006054, hsa_circ_100219 and hsa_circ_406697 were used 
in combination. This study provides evidence that circRNAs are differentially 
expressed in breast cancer and are important in carcinogenesis because they 
participate in cancer-related pathways and sequester miRNAs.