P08.19 Application of SDC2 and Septin9 gene methylation detection in colorectal cancer diagnosis and immunotherapy efficacy assessment

S D C2 gene encodes the transmembrane proteoglycan molecule Syndecan-2. Syndecan-2 protein affects the proliferation, migration and invasion of colorectal cancer (CRC) cells by participating in the regulation of cell adhesion, tissue differentiation and angiogenesis. Plasma methylated Septin9 gene has been shown to be a sensitive and specific biomarker for the detection of CRC, which is involved in apoptosis, pseudopod projection, tumor cell migration and invasion. The aim of this study is to validate the value of SDC2 and Septin9 gene methylation detection in the diagnosis and immunotherapy efficacy evaluation of colorectal cancer.A total of 102 patients were included in the study. Real-time PCR was used to detect the methylation levels of SDC2 gene in feces and Septin9 gene in blood. The clinical diagnostic accuracy of SDC2 kit was evaluated in patients with gastrointestinal benign lesions, gastrointestinal tumors and healthy subjects. Combined detection of SDC2 and Septin9 can improve the detection rate of CRC. The SDC2m levels of 26 patients with partial remission or stable disease after immunotherapy and 32 patients with complete remission after radical surgery were analyzed.For eight healthy subjects with negative colonoscopies, the true negative rate was 100%. Data from 72 patients with CRC were evaluated, revealing a sensitivity of 89.1% ( 41/46; 95% CI: 0.798-0.985) for untreated CRC. In patients who had received immunotherapy and showed partial response or stable disease, the sensitivity of SDC2 was 46.2% (12/26; 95% CI: 0.256-0.667). The sensitivity of Septin9 for CRC detection was 88.2% (15/17; 95% CI: 0.712-1.053). By combining two tests, 94.1% (16/17; 95% CI: 0.816-1.066) of CRC cases could be detected. Sensitivity was 89.1% in patients with untreated CRC and 46.2% in those with partial response or stable disease after immunotherapy. There was a significant difference in the positive rate of SDC2m between the two groups (P < 0.001). Among the 32 patients with colorectal cancer who underwent radical surgery, 93.8% (30/32) of the colorectal cancer patients who were initially positive for SDC2m were negative.Detection of SDC2m in untreated CRC patients has high sensitivity and has the potential to become a non-invasive diagnostic tool for CRC. Combination of Septin9 and fecal SDC2 could improve the detection rate of SDC2 in non-dominant population.The methylation level of SDC2 may be helpful for postoperative follow-up, prediction of recurrence and the efficacy of immunotherapy after radical surgery for CRC.