Assimilation of FIT into primary and secondary care diagnostic pathways will lead to an increased prominence of the investigation in the diagnosis of colorectal cancer (CRC). Questions remain about whether serial FIT analysis improves accuracy, and what factors affect it.

Our study will analyse FIT results in recently diagnosed CRC patients to determine the risk of a false-negative FIT result and evaluate whether repeated analysis improves diagnostic accuracy. The study aims to advise on whether there is an optimal interval between sample collection to improve diagnostic accuracy and whether any patients are at risk of a false negative based on demographics, medications or other pathological factors.

Colorectal cancer (CRC) remains a leading cause of cancer death in the UK and worldwide. Improving outcomes depends in part on achieving earlier diagnosis of the disease.

The Faecal Immunochemical Test (FIT) is replacing the less accurate Faecal Occult Blood Test (FOBT) in the UK and has the potential to help achieve earlier stage diagnosis of CRC. Whilst FIT has been validated as a screening test for the Bowel Cancer Screening Programme (BCSP), its role in diagnosing CRC in symptomatic populations is yet to be defined.

Nottingham is a pioneering centre using FIT to stratify risk and determine first-investigation in its two-week-wait (2WW) pathway. To optimise use of FIT and minimise the chance of missed cancers, this project aims to better understand variation of FIT results over time and how certain factors affect FIT result.

Much of the literature has focused on the evaluation of FIT in an asymptomatic population, which is inherently low risk (4,6,7). Expanding use of FIT to stratify risk and guide investigations for cancer in (higher risk) symptomatic populations necessitates a thoroughly evaluated testing strategy. At present there is insufficient information to advise on "negative" FIT results in symptomatic patients. This study will comprehensively measure FIT variation over time in patients with the target condition (CRC) and help answer whether additional samples are likely to improve accuracy of FIT.

Risk factors for false positives and false negatives have been previously identified but are not widely established (4). Our study will record the presence of these risk factors, and evaluate their effects on FIT-positivity with subsequent statistical analysis.

Inclusion Criteria:

• Histologically confirmed colorectal cancer

Exclusion Criteria:

• Less than 18 years old
• Not attending Nottingham University Hospitals for diagnosis/treatment (attending another trust)
• No histological diagnosis of colorectal cancer
• Unable to provide informed consent - for example due to language barriers or lacking capacity to join study

200 patients will be recruited to the study. Nottingham University Hospitals NHS Trust diagnoses approximately 500 CRCs per year, yielding an available population pool of 1000 patients in the study period. A sample size of 200 participants (returning 1000 samples in total) represents a realistic recruitment target.

No plan to share individual participant data