Colorectal cancer remains a significant cause of mortality worldwide. The CRC incidence and mortality are actually increasing despite recent advances in surgery, radiotherapy and chemotherapy . And despite curative surgical resection of the primary tumor, 40–50% of the patients ultimately die of metastasis . Due to fact that CRC usually appear obvious symptoms until it progresses to advanced stages, so the implementation of screening programs aimed at early detection is essential to reduce incidence and mortality rates. Currently, The most common clinical imaging screening methods is colonoscopy. However, there were some limitations for this method such as invasion character, and causing abdominal pain . In addition, the sensitivity and specificity of the laboratory detection methods, such as stool test, occult blood immunology and tumor markers detection are poor . Therefore, looking for a novel biomarker for CRC non-invasive examination is of important clinical significance.
Recent studies indicated that miRNAs, which are non-protein-coding small RNAs, are involved in cancer progression and metastasis. MiRNA expression signatures have been shown to be promising biomarkers for understanding the tumorgenesis of a wide array of human cancers [25, 26]. Accordingly, studies speculated that some tumors secretion circulation miRNAs in serum or plasma could be molecular markers for clinical diagnosis of CRC. Ng et al. found that the high expression of miR-17-3p and miR-92a was closely related to CRC, and the expression levels of plasma miR-17-3p and miR-92a decreased significantly after surgery . The results confirmed abnormal expression of miRNAs in the plasma circulation. Huang et al. further confirmed the diagnosis potential of miR-92a, indicated that the plasma of patients with CRC contains high levels miR-92a, and its diagnostic sensitivity and specificity are consistent with the results of Ng et al. .
Previous research confirmed that miR-124 was a tumor suppressor in various types of cancers, including glioblastoma, hepatocellular carcinoma, medulloblastoma, and gastric cancer [29, 30]. Xie et al.  reported that miR-124 was down-regulated in gastric cancer cells and specimens and it inhibited cancer cell proliferation and induced apoptosis by targeting enhancer of zeste homolog 2 in gastric cancer. The expression level and mechanism of miR-124 have also been investigated in breast cancer. Han et al.  found that miR-124 played a critical role in inhibiting the invasive and metastatic potential of breast cancer cells. Moreover, the previous study also reported the function of miR-124 in colorectal cancer, it was significantly downregulated in CRC and interacted with ROCK1 to regulate the tumor cell proliferation . However, the diagnostic value of miR-124 in CRC was not studied.
This study is the first to demonstrate the potential role of serum miR-124 in the early detection of CRC. The data showed that patients with CRC had significantly lower serum miR-124 levels compared with healthy control subjects. To evaluate the relationship between serum miR-124 and CRC progression, we further analyzed the correlation between miR-124 expression and clinical pathological features of CRC. The results demonstrated that there is a strong correlation between serum miR-124 levels and tumor size, invasion depth, lymph node metastasis, and TNM stage. These observations suggested a correlation between increased expression of miR-124 and clinical progression in CRC. Furthermore, we established the ROC curve to evaluate the diagnostic value of miR-124 in CRC. These results indicate that down-regulation of serum miR-124 may occur in the early stage of CRC and can serve as a potential biomarker of early diagnosis in CRC.