Objective To detect the methylation status of Septin 9 in the peripheral blood of patients with colorectal cancer (CRC) and analyze the relationship between the methylation of Septin 9 and CRC.

Methods A total of 120 patients with CRC were selected as research objects, and the relationship between the methylation status of Septin 9 in the peripheral blood and the medical materials was analyzed; the serum exosomes isolated from patients with CRC and healthy people were used to treat the CRC cells, and the proliferation and apoptosis of CRC cells were detected.

Results A total of 1 586 people with health examinations were screened for Septin 9, and 56 of whom were positive for methylation of Septin 9, with a positive rate of 3.5%. Among patients with Septin 9 positive, there were 20 cases (35.7%) with abnormal gastrointestinal status (gastrointestinal inflammation or polyps), while only 5.4% (83/1 530) of patients with Septin 9 negative had abnormal gastrointestinal status, which indicated that the methylation status of Septin 9 in the peripheral blood was closely related to the gastrointestinal status. Among 120 CRC patients, the positive rate of methylation of Septin 9 was 78.4% (73/93); in the comparison of different differentiation degrees, the positive rates of Septin 9 methylation in patients with highly differentiated, moderately differentiated and poorly differentiated CRC were 52.6% (10/19), 79.7% (59/74) and 88.9% (24/27) respectively, and the positive rate of Septin 9 methylation in peripheral blood of patients with poorly differentiated CRC was significantly higher than that of patients with highly differentiated CRC (P=0.006). The sensitivity and specificity of Septin 9 methylation in the peripheral blood were 72.3% and 92.5% respectively. Western blot results showed that the expression of Septin 9 in the exosomes of CRC patients was significantly lower than that in the normal people, while the methylation level of Septin 9 in the exosomes was significantly higher than that in the healthy people (P=0.009, 0.003). The results of this study showed that serum exosomes of CRC patients could significantly promote cell proliferation and inhibit cell apoptosis (P < 0.05 or P < 0.01).

Conclusion Septin 9 can be used as a marker for early screening of CRC, and the mechanism of Septin 9 may be the proliferation and apoptosis resistance of CRC induced by serum exosomes in patients with CRC.