Colorectal cancer risk stratification using a polygenic risk score in symptomatic patients presenting to primary care – a UK Biobank retrospective cohort study
Authors: Mallabar-Rimmer Bethan , Merriel Samuel WD , Webster Amy P , Wood Andrew R , Barclay Matthew , Tyrrell Jessica , Ruth Katherine S , Thirlwell Christina , Oram Richard , Weedon Michael N , Bailey Sarah ER , Green Harry D 
Published: December 2023

Colorectal cancer (CRC) is a leading cause of cancer mortality worldwide. Accurate cancer risk stratification approaches could increase rates of early CRC diagnosis, improve health outcomes for patients and reduce pressure on diagnostic services. The faecal immunochemical test (FIT) for blood in stool is widely used in primary care to identify symptomatic patients with likely CRC. However, there is a 6–16% noncompliance rate with FIT in clinic and ∼90% of patients over the symptomatic 10µg/g test threshold do not have CRC.

A polygenic risk score (PRS) quantifies an individual’s genetic risk of a condition based on many common variants. Existing PRS for CRC have so far been used to stratify asymptomatic populations. We conducted a retrospective cohort study of 53,112 UK Biobank participants with a CRC symptom in their primary care record at age 40+. A PRS based on 207 variants, 5 genetic principal components and 24 other risk factors and markers for CRC were assessed for association with CRC diagnosis within two years of first symptom presentation using logistic regression. Associated variables were included in an integrated risk model and tested for ability to predict CRC diagnosis within two years, using receiver operating characteristic area under the curve (ROCAUC) and Akaike information criterion (AIC).

An integrated risk model combining PRS, age, sex and patient-reported symptoms was highly predictive of CRC development (ROCAUC: 0.80, 95% confidence interval: 0.78– 0.81). This model has the potential to improve early diagnosis of CRC, particularly in cases of patient non-compliance with FIT.

Lay Abstract

Bowel cancer is one of the most common types of cancer worldwide, and patients diagnosed earlier have a much better chance of survival. Finding ways to predict which people are at risk of developing bowel cancer is therefore a research priority.

In this study, we used genetics and information about patients (such as age and sex) to predict which patients are at high risk of developing bowel cancer within two years of seeing their GP with a symptom. We tested 30 risk factors and identified eight that were more common in patients who developed bowel cancer shortly after experiencing symptoms.

These eight risk factors included: older age, being male, larger waist circumference, smoking, higher inherited genetic risk, and presence of two symptoms – change in bowel habit (including constipation or diarrhoea) and/or bleeding from the rectum. On the other hand, stomach pain was the symptom which occurred least in people who developed bowel cancer.

Six of the above risk factors, when combined into one measure of risk (called ‘a risk model’) were good at predicting which patients would develop bowel cancer shortly after symptoms. These factors included age, sex, genetic risk, bleeding from the rectum, change in bowel habit and stomach pain.

This risk model could help doctors decide which symptomatic patients to send for bowel cancer testing. This would allow earlier detection of bowel cancer which would improve outcomes for patients.