Study Of The Methylation Change Of SFRP2 Gene In Fecal DNA As A Potential Biomarker For Colorectal Cancer Noninvasive Screening

Objective:Colorectal cancer(CRC)is a malignant lesion occurres when the intestinal epithelium suffer from carcinogenic agents such as environmental or genetic factors,and is the third most common cancer worldwide. It takes ten years average that colonic epithelial cells developed from the adenomatous dysplasia neoplasia to carcinoma, and the identifiable adenoma development into invasive carcinoma needs five years, which provided sufficient time for early screening and prevention. CRC is most effectively treated when diagnosed at an early stage, but the early stage of CRC is mostly symptomless as well as delitescence nature. Approximately 40% of CRCs are diagnosed with localized disease, which have approximately a 70%~90% five-year survival rate after curative surgery. However, the prognosis worsens with advancing stage, and only 5% of patients diagnosed with distant metastases survive 5 years. With the potential of both reducing incidence from CRC as well as enhancing primary prevention through detection and removal of lesions that could potentially develop into cancer, early detection of CRC will increase survival the most. Therefore, the need for early detection is clear for high-risk groups, and an effective screening test would have substantial clinical benefits. It is difficult to reduce CRC incidence rate by changing people's way of life. Whereas CRC screening will moderate decline in mortality, and it may decrease the incidence of CRC through detection and removal of colorectal adenoma (early less invasive surgical treatment or endoscopic resection). Now that most of the early detection technologies such as fecal occult blood test, barium enema and electronic colonoscopy were low accuracy, high cost, invasive, non-compliance of patients, even serious complications such as intestinal bleeding and perforation and et al. So these methods is not suitable for screening. Therefore, exploration of a safe, reliable, specific, effective early CRC screening methods is the Urgent medical profession problem to be solved. CpG island hypermethylation of the tumor suppressor gene is the most common molecule change of CRC, and hypermethylation of the several genes is closely related to occurrence and development of CRC. Methylation changes often occurred in the early stage of CRC, which is easily detected in the faeces of patient. The characteristic and procedure of DNA methylation changes as tumor markers for the clinical diagnosis is superior to mutation detection. Thus, DNA methylation is closely correlated with early diagnosis, staging, treatment and prognosis of CRC and even can be used for large crowds screening, which has become a new research hot spots for early detection of CRC. In recent years, several studies have identified frequent promoter hypermethylation and silencing of the secreted frizzled-related protein 2 (SFRP2) genes in CRC, which is an early frequently event in colorectal tumorigenesis. This study is to investigate the feasibility of detecting hypermethylated SFRP2 gene in fecal DNA as a non-invasive screening tool for CRC by detecting faecal SFRP2 gene methylation status in patients with colorectal carcinoma and benign disease.METHODS:Methylation-specific PCR assay (MSP) was performed to analyze SFRP2 gene promoter methylation status in a blinded fashion in tumor tissues and in stool samples taken from 69 CRC patients preoperatively and at the 9th postoperative day, 34 patients with adenoma≥1 cm, 26 with hyperplastic polyp, and 30 endoscopically normal subjects. Simultaneously the relationship between hypermethylation of SFRP2 gene and clinicopathological features was analyzed. RESULTS:SFRP2 gene was hypermethylated in 91.3% (63/69) CRC, 79.4% (27/34) and 53.8% (14/26) adenoma and hyperplastic polyp tissues, and in 87.0% (60/69), 61.8% (21/34) and 42.3% (11/26) of corresponding fecal samples, respectively. In contrast, no methylated SFRP2 gene was detected in mucosal tissues of normal controls, while two cases of matched fecal samples from normal controls were detected with hypermethylated SFRP2. A significant decrease (P < 0.001) in the rate of hypermethylated SFRP2 gene was detected in the postoperative (8.7%, 6/69) fecal samples as compared with the preoperative fecal samples (87%, 60/69) of CRC patients. Moreover, no significant associations were observed between SFRP2 hypermethylation and clinicopathological features including sex, age, tumor stage, site, lymph node status and histological grade, etc.CONCLUSION:Hypermethylation of SFRP2 gene in fecal DNA is a novel molecular biomarker of CRC and carries a high potential for the remote detection of CRC and premalignant lesions as noninvasive screening method.