An exploration of metachronous colorectal lesion predictors from a bowel screening population

Abstract

The rising incidence and mortality rates of colorectal cancer (CRC) continue to impact patients and burden healthcare systems worldwide. Multiple factors contribute to increasing CRC risk and, while modifiable ones such as improving diet, and smoking cessation are within an individual’s control, non-modifiable factors such as age and a genetic propensity for CRC remain major causes of the disease. This led to many countries adopting national screening programs to promote the early detection and prevention of CRC. Many modalities can be used for screening, but several countries (including the United Kingdom (UK)) begin with a quantitative faecal immunochemical test (qFIT) and, should a positive result be found, a colonoscopy is recommended. Not only do screening colonoscopies detect CRC but also find pre-malignant polyps from which most CRC is derived. These are removed opportunistically as a mode of prevention; however the presence of polyps is associated with ongoing future risk of polyps and CRC, leading to the need for surveillance. In 2020, the British Society for Gastroenterology published updated guidelines (BSG2020 Guidelines) for the surveillance of patients who underwent a screening colonoscopy. They define a “high-risk” patient as one whose colonoscopy revealed two or more polyps where at least one was advanced, a serrated polyp larger than 1cm or with dysplasia, an adenoma larger than 1cm or with high-grade dysplasia, or five or more polyps. According to BSG2020 Guidelines, “high-risk” patients are recommended to undergo a second colonoscopy for surveillance of metachronous polyps or CRC within three years of the screening colonoscopy. However, with only 20-50% of “high-risk” patients developing metachronous polyps, coupled with the endoscopy services backlog in the UK, these risk stratification guidelines are not sufficient. This thesis aimed to identify a suitable tool to improve the current BSG2020 Guidelines for risk stratification within a bowel screening population. Initially, Fusobacterium nucleatum, was investigated with relation to the detection of metachronous polyps or CRC, through detection by a novel technique, TempO-Seq™. Numerous evidence of the involvement of F. nucleatum in CRC is available, implicating it in supporting tumorigenesis and metastasis. F. nucleatum+ patients revealed an immune-oriented whole tissue transcriptomic profile, however, spatial transcriptomics revealed a poor adaptive immune response in those patients. Similarly, there was no association between lymphocytic markers (CD3+ T cells, CD4+ T cells, and CD8+ T cells) and the detection of metachronous polyps or CRC in patients with a known F. nucleatum status, although the stimulation of patient-derived organoids with inflammatory cytokines led to an increase in cell viability. Ultimately, F. nucleatum in this cohort was not associated with the detection of metachronous polyps or CRC. However, mutational analysis of adenomas from these patients revealed mutations in multiple Wnt pathway-associated genes. At the protein level, E-Cadherin and β-Catenin were not associated with the detection of metachronous polyps or CRC. However, the high expression stemness marker and Wnt regulator SOX9 in the cytoplasm was associated with the detection of metachronous polyps or CRC. Patients with high SOX9 protein expression demonstrated a proliferative transcriptomic profile, with multiple anti-microbial pathways being positively enriched. Finally, the addition of SOX9 protein expression to current BSG2020 Guidelines significantly improved risk stratification. This research provides a basis for the use of additional stratification methods to improve the rate of prediction of metachronous polyps or CRC, using simple well-established methods like immunohistochemistry