Bowel cancer (colorectal cancer) is the 4th most common cancer in Scotland. Approximately 4,000 cases are diagnosed annually. Cancer-related deaths in Scotland are higher than other UK nations. Improving the early detection of bowel cancer, and therefore survival, is important.

The majority of bowel cancers are diagnosed within secondary-care (colorectal surgery unit). Upon GP referral to secondary-care, patients provide stool samples which are analysed for microscopic blood (FIT; faecal immunohistochemical test). Patients with a single positive result are more likely to have bowel cancer (0.2% risk if no blood detected, but 8.4% if detected). A positive test triggers further investigation, either CT scan or colonoscopy depending on the result. Currently, colonoscopy and radiology services throughout Scotland are under significant pressure causing delays.

Only 2% of patients referred to secondary-care are diagnosed with bowel cancer, and most colonoscopies performed do not yield significant findings. We have shown that performing two repeated FITs upon referral improves cancer pickup rate (sensitivity) and reduces missed cancers. We successfully implemented this in NHS Lothian and contributed to national guidelines.

This study will undertake a comprehensive retrospective review of the double-FIT urgent suspicion of bowel cancer pathway within NHS Lothian, from April 2022 (date of pathway inception) to August 2025, including around 25,000 patients that have been managed through the pathway. We will calculate key performance indicators and diagnostic accuracy of the pathway. Health economic analysis will determine cost-per-diagnosis. Risk factors for bowel cancer in this patient cohort will be identified to develop a support tool for primary and secondary-care. These results will be used to develop a future pathway to optimise pathway efficiency and cancer detection.

Design:

This is a retrospective observational cohort data-analysis study of patients managed within the NHS Lothian colorectal cancer (CRC) urgent suspicion of cancer (USoC) pathway and patients referred urgently to the Colorectal department from April 2022 to August 2025. April 2022 corresponds to the start of double FIT testing within the pathway. 5-year follow-up will be included (up to August 2030) to include 5-year cancer outcomes.

Methods:

Patients will be identified from our pathway. Estimated ~25,000 patients will be included. Data will be collected on patient characteristics, past medical and prescribing history, hospital presentations and investigation outcomes, cancer outcomes and mortality data. Linkage to relevant patient datasets will be required.

A service review of the USoC/urgent pathway will focus on key performance indicators such as time to diagnosis and treatment, as well as patient journey pathways (Sankey plots) and re-referral rates.

Furthermore, data will be analysed using standard methods such as odds-ratio multivariate logistic regression to determine any significant associations which enrich for CRC and significant bowel pathology in this patient group. Significant bowel pathology includes advanced adenoma, advanced colorectal neoplasia and inflammatory bowel disease (IBD). Importantly, the modelling will only utilise readily available information from the electronic health record (EHR) such as age, sex, blood haemoglobin, BMI and SIMD to improve pre-test probability by restricting the target population.

Markov models will be formed as part of the health economic analysis, and the financial cost per case detected within the pathway will be calculated. We will explore the impact of waiting times on disease progression and the associated impact on the financial costs of treatment and patient quality of life.

Results from the above analyses will be incorporated into a decision-flow as guidance for referrals to secondary-care.

Sample size calculation:

To perform regression analysis, at a significance level of 0.05, medium size effect and 10 predictors, 170 cases of CRC are required. Our database of ~25,000 patients has approximately 500 cases of CRC. There will be minimal anticipated drop-out. Therefore our required sample size will be achievable.22

Proposed analyses:

Standard summary statistics of the pathway will be reported (means, standard deviations, medians, inter-quartile range). Multivariate logistic regression will be performed to determine risk-factors significant for CRC at different FIT levels. Subgroup analyses will take place within different FIT result thresholds (<10, 10-79, >79 µgHb/g) as well as between cancer and non-cancer patients, and for other significant bowel pathology. Long-term outcome data will be analysed, up to 5 years.

Furthermore, a service evaluation of the USoC/urgent pathway will focus on key performance indicators such as time to diagnosis and treatment, as well as patient journey pathways (Sankey plots) and re-referral rates. Markov models will be formed as part of the health economic analysis, and the financial cost per case detected within the pathway will be calculated. We will explore the impact of waiting times on disease progression and the associated impact on the financial costs of treatment and patient quality of life. The rate of interval cancers over long-term follow-up will be calculated.

We do not anticipate a significant amount of missing data. Data entries will be removed due to missing data on an analysis-by-analysis basis.

Inclusion Criteria:

Patients managed within the NHS Lothian CRC USoC/urgent pathway (including urgent referrals) due to 'red-flag' symptoms concerning of CRC from April 2022 to August 2025.

Exclusion Criteria:

• Under the age of 18.
• History of inflammatory bowel disease.
• Under polyp surveillance.
• Previous diagnosis of CRC.

Adults referred to secondary-care with 'red-flag' gastrointestinal symptoms concerning for CRC.

There is no plan to share IPD due to patient numbers and confidentiality