The investigators hypothesize that gut microbiome composition and the four bacterial gene markers (M3) show dynamic changes after endoscopic resection of advanced neoplasia, some key bacteria are associated with restoration of gut microbiome after endoscopic resection.

Colorectal cancer (CRC) is one of the most common cancers in Hong Kong with more than 5,500 new cases annually. The majority of CRC cases are derived from benign colorectal adenomas through the process of adenoma-carcinoma sequence. Since this process takes several years, early detection and endoscopic resection of colorectal adenomas are important to reduce the incidence and mortality of CRC. Currently, colonoscopy is the gold standard for detection for colorectal adenomas. Endoscopic resection including endoscopic submucosal dissection (ESD) and endoscopic mucosal resection (EMR) can serve as minimally invasive treatment options for colorectal neoplasia. Compared with EMR, due to the general association with higher rates of en bloc, R0, and curative resections and a lower rate of local recurrence, ESD is an established and effective treatment modality for advanced adenoma (AA) and early-stage CRC.

Increasing studies showed a close crosstalk between the gut microbiome and colorectal neoplasia. Altered microbiome environment is associated with the initiation and progression of CRC and its precancerous lesions. Most studies focused on the gut microbiota changes in individuals with CRC and adenomas, and the potential microbial role in the progression of colorectal neoplasia. Conversely, the potential influence of CRC or adenomas on the gut microbiota is unclear. Only one study has depicted microbiota changes after the endoscopic removal of colorectal adenomas with limited follow up timepoints. Due to a high rate of recurrence of colorectal adenomas after endoscopic removal, surveillance colonoscopy is required depending on the size, number, and histology of polyps in the index coloscopy. Apart from these risk factors, reestablishment of gut microbiome after polyp resection may also play a role in the recurrence of adenomas.

Recently, a panel of bacterial gene markers including "m3" from Lachnoclostridium, Fusobacterium nucleatum (Fn), Bacteroides clarus (Bc) and Clostridium hathewayi (Ch) showed high diagnostic accuracy for CRC (82.3%) and adenomas (64.2%). The combination of these four bacterial gene markers (known as M3) has also been proven to be useful in detecting adenoma recurrence after polypectomy in a retrospective study. However, how these bacteria markers change after polypectomy and whether there are some associations between changes of bacteria gene markers and post resection restoration of the gut microbiome remain unclear.

This pilot study aims to determine serial gut microbiome composition changes, and changes in levels of the panel of four bacterial gene markers (M3) after endoscopic resection of colorectal advanced neoplasia, and factors associated with restoration of gut microbiome composition after endoscopic resection.

Inclusion Criteria:

• Subjects require endoscopic resection (e.g. endoscopic mucosal resection or endoscopic submucosal dissection) for advanced adenoma or early-stage colorectal cancer;
• Aged 18-90 years old;
• Written informed consent obtained.

Exclusion Criteria:

• Absolute contraindications to colonoscopy (e.g. perforation, intestinal obstruction, unstable cardiopulmonary status);
• Contraindications to endoscopic resection (e.g. active gastrointestinal bleeding, uninterrupted anticoagulation or dual antiplatelets);
• Known pregnancy or lactation;
• Advanced comorbid conditions (defined as American Society of Anesthesiologists grade 4 or above);

Subjects with known colorectal advanced neoplasia