Background and Aims: Circular RNAs are a class of important regulatory elements that are involved in many cancer processes. It was reported that circular RNA FBXW7 (RNA circFBXW7) plays a tumor suppressor role in glioma through encoding a novel protein. However, its function and action mechanism in triple-negative breast cancer (TNBC) is still unclear. Therefore, this study was conducted to investigate the role of circFBXW7 in TNBC and its clinical significance. 
Methods: The fresh specimens of tumor tissues from 240 TNBC patients and their clinical data were collected. the related prognosis data were also collected. The expression levels of circFBXW7 in these samples were detected by qRT-PCR, the relationship between circFBXW7 expression and the prognosis of TNBC patients was analyzed by Kaplan-Meier method, and the prognostic factors for TNBC patients were determined by Cox regression analysis. In TNBC cell lines MDA-MB-231 and HCC1806 after circFBXW7 over-expression, the changes in proliferation, migration and invasion abilities as well as miR-197-3p expression were examined by CCK8 assay and Transwell chamber assay. In above two types of cells after circFBXW7 knockdown and simultaneous miR-197-3p inhibitor transfection, the changes in proliferation and invasion abilities were measured by colony formation assay and Transwell chamber assay, respectively. 
Results: The average expression level of circFBXW7 in the tumor tissues from the 240 TNBC patients was 1.043±0.268. Using 1.043 as a threshold value, the results of grouped analysis showed that both overall survival and disease-free survival in patients with low circFBXW7 expression were significantly shorter than those in patients with high circFBXW7 expression (both P<0.05); the circFBXW7 expression, histological grade and TNM classification were independent influencing factors for the prognosis of TNBC patients (all P<0.05). The results of cytological studies showed that the proliferation, migration and invasion abilities as well as the miR-197-3p expression levels of MDA-MB-231 and HCC1806 cells were significantly reduced after circFBXW7 over-expression (all P<0.05); the increased proliferation and invasion abilities of MDA-MB-231 and HCC1806 cells induced by circFBXW7 knockdown were reversed by simultaneous miR-197-3p inhibitor transfection (both P<0.05).
Conclusion: The circFBXW7 expression plays a suppressing role in TNBC, and the mechanism may be associated with its competitive binding miR-197-3p and thereby inhibit the proliferation and invasion of TNBC cells. It may be a novel prognostic biomarker and a potential therapeutic target for TNBC.