Abstract Background The detection rate of methylated Septin9 (mSEPT9) in colorectal cancer (CRC) is varied greatly across the studies. This study aimed to evaluate the diagnostic ability of mSEPT9 in CRC, and compare the diagnostic efficacy with fecal immunochemical test (FIT). Methods 326 subjects from four centers were prospectively recruited, including 179 CRC and 147 non-CRC subjects. The plasma was collected for mSEPT9 and CEA, AFP, CA125, CA153 and CA199 test, and fecal samples for FIT tests. Sensitivity, specificity and area under the curve (AUC) of receiver operating characteristic curve were calculated to evaluate the diagnostic value of each biomarker. Results The positive rate in mSEPT9 and FIT, and the level of CEA, CA125 and CA199 were significantly higher in CRC compared with non-CRC subjects. The mSEPT9 positive rate was not associated with TNM stage and tumor stage. The sensitivity, specificity and AUC of mSEPT9 in diagnostic CRC were 0.77, 0.88 and 0.82, respectively, while the value in FIT was 0.88, 0.80 and 0.83, respectively. mSEPT9 and FIT have higher AUC value than that of CEA, CA125 and CA199. Combination of both mSEPT9 and FIT positive increased sensitivity and AUC to 0.98 and 0.83, respectively, but the specificity was declined. mSEPT9 has a slightly low sensitivity in diagnosis of colon cancer (0.87) compared with rectal cancer (0.93). Conclusion mSEPT9 demonstrated moderate diagnostic value in CRC detection, which was similar to the FIT but superior to the CEA, CA125 and CA199. Combination of mSEPT9 and FIT further improved diagnostic sensitivity in CRC. Trial registration: ChiCTR2000038319.
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