USING TWO DIFFERENT CUT-OFF LEVELS OF FECAL IMMUNOCHEMICAL TEST IN THE HIGH-RISK AND NON-HIGH-RISK INDIVIDUALS TO MAINTAIN THE HIGH-RATE DETECTION OF ADVANCED COLORECTAL NEOPLASIA: A POPULATION-BASED COLORECTAL CANCER SCREENING IN THAILAND

Introduction: The ultimate goal of colorectal cancer (CRC) screening is to prevent CRC by detecting advanced adenomas that potentially progress to CRC. Previous studies demonstrated that the Asia-Pacific Colorectal Screening (APCS) score could select more advanced neoplasia (AN) subjects and reduce the number needed to screen (NNS). Using the recommended cutoff FIT for the average-risk individual at 100 ng/ml could have missed AN in the high-risk individuals. Hypothetically, using the lower cutoff of FIT in those with high risk may improve the sensitivity for AN detection. Therefore, we aimed to evaluate the performance of the cutoff FIT of 25 ng/ml in the high-risk population and the cutoff FIT of 100 ng/ml in the non-high-risk population.
Methods: We conducted an organized CRC screening program in four districts in Thailand. Asymptomatic subjects aged 50-75 were invited and interviewed by the village health volunteer. Using the APCS score (i.e., age, male, smoking, and a first-degree relative with CRC), subjects were stratified into the high-risk or non-high-risk group. The positive FIT was called in the high-risk group with quantitative FIT using the cutoff ≥25 ng/ml (FIT25) and ≥100 ng/ml (FIT100) in the non-high-risk group. Positive FIT subjects were invited for colonoscopy. We assessed the positive predictive value (PPV) and NNS to detect AN—AN comprised of advanced adenoma and CRC. We compared the two cutoffs (FIT25/100) in high and non-high-risk individuals and the single cutoff in all individuals (FIT100). The analysis population was intention-to-treat.
Results: Of 12,000 invited subjects, 10262 subjects (85.5%) participated in the FIT program. The mean age was 60 years, and 33.7% were male. Of those, 8578 (83.6%) screenees were classified as non-high-risk, and 1684 (16.4%) were high-risk. The return rate of FIT was 99.6% (n=10221). The acceptance rate for colonoscopy was 68.3% (n=915). The positivity rate of FIT25/100 was 13.1% (n=1340) in the FIT25/100 group and 9.4% (n=961) in the FIT100 group (p<0.001). In the FIT25/100 and FIT100 groups, AN and CRC were detected in 158 and 34 screenees and 133 and 33 screenees, respectively. The PPV for AN (11.8% vs. 13.8%, p=0.17) and CRC (2.5% vs. 3.4%, p=0.21) were not significantly different between the FIT25/100 and FIT100 groups. The NNS to detect one AN in FIT25/100 was 64.9 (95%CI, 63.7 - 66.2) and significantly lower than that of in FIT100 (77.2 (95%CI, 75.7 - 78.7); p<0.001) (Table 1). This strategy reduced 15.8% in NNS to detect AN compared to FIT100 for all individuals (p<0.001).
Conclusion: Using a lower FIT cutoff in the high-risk individuals showed better performance with lower NNS while maintaining high PPV for AN and CRC detection compared to using a high cutoff for all individuals. This strategy could reduce the workload in CRC screening in limited-resource countries.