Plasma circular RNA panel acts as a novel diagnostic biomarker for colorectal cancer

Background: Colorectal cancer (CRC) is one of the most common cancers worldwide, and emerging lines of evidence have implicated circular RNAs (circRNAs), a novel class of endogenous noncoding RNAs, in CRC development. However, whether plasma circRNAs might be novel diagnostic biomarkers for CRC remains unclear. Methods: We investigated the plasma levels of selected circRNAs by quantitative real-time PCR (qRT-PCR). The presence of the candidate circRNAs was confirmed through RNase R assays, qRT-PCR and DNA sequencing, and their diagnostic value was evaluated using a receiver operating characteristic (ROC) curve. Results: The plasma levels of three circRNAs (circ-CCDC66, circ-ABCC1 and circ-STIL) were significantly decreased in CRC patients (n=45) compared with healthy controls (n=61). The ROC curve analysis showed that the area under the ROC curve (AUC) of the three-circRNA panel was 0.780, which is higher than that of traditional protein biomarkers, such as carcinoembryonic antigen (CEA) and carbohydrate antigen 19-9 (CA19-9). Combining the circRNA panel with CEA and CA19-9 might improve the ability to diagnose CRC (AUC=0.855). In addition, the plasma circ-ABCC1 level was related to tumor growth and progression, and the plasma circ-CCDC66 and circ-ABCC1 levels were decreased in precursor lesions of CRC, including colon adenomas and adenomatous polyps. More importantly, circC-CDC66 and circ-STIL were found to be useful for diagnosing early-stage CRC, and the three-circRNA panel improved the ability to diagnose CEA-negative and CA19-9-negative CRC. Conclusion: Our study provides the first identification of a panel of three plasma circRNAs that could serve as a novel and independent diagnostic biomarker for CRC.