RATES AND PREDICTORS OF POST-COLONOSCOPY COLORECTAL CANCER IN FECAL IMMUNOCHEMICAL TEST-POSITIVE INDIVIDUALS

Background
Colonoscopy with polypectomy has been shown to reduce the incidence and mortality of colorectal cancer (CRC) through the removal of precancerous polyps. The United States Multi-Society Task Force (USMSTF) on CRC, recommends colonoscopy or annual FIT as tier 1 screening tests for CRC. Individuals with a positive FIT are recommended to undergo colonoscopy and are shown to have higher rates of advanced adenomas as compared to average-risk individuals undergoing screening colonoscopy. However, the incidence of post-colonoscopy CRC (PCCRC) in FIT-positive individuals is not well studied. The aim of our study is to evaluate the incidence and predictors PCCRC in FIT-positive individuals using an integrated nationwide database of United States veterans.

Methods
Data was obtained from the Veterans Health Administration (VHA) Corporate Data Warehouse (CDW) using Structured Query Language (SQL). Individuals who underwent their first colonoscopy after a positive FIT between January 2015 and August 2023 were included. Pathology records and ICD-10 codes were queried using Natural Language Processing to identify individuals diagnosed with PCCRC (defined as CRC diagnosed ≥6 months after initial colonoscopy after FIT). Polyp subtypes at initial colonoscopy were recorded, including tubular adenomas (TAs), tubulovillous adenomas (TVAs), adenomas with high-grade dysplasia (HGD), sessile serrated lesions (SSLs), and traditional serrated adenomas (TSAs).

The primary study outcome was the incidence of post-colonoscopy CRC in FIT-positive individuals. Secondary outcomes were time from baseline colonoscopy to PCCRC and predictors of PCCRC in FIT-positive individuals. Logistic regression was utilized to examine the multivariate relationships between each independent variable of interest and PCCRC.

Results
A total of 52,599 individuals underwent colonoscopy within 12 months of a positive FIT. The mean age was 62.5 years and 93.4% were male. The prevalence of detected polyp subtypes was as follows: TA/TVA 40.2%, adenoma with HGD 1%, SSL 6.1%, concomitant TA/TVA and SSL 4.1%. Invasive adenocarcinoma was detected in 1.1% of cases at the time of initial colonoscopy after positive FIT. Over a median follow-up of 25.5 months [IQR: 12-45], we identified 192 cases of PCCRC. Patient demographics and initial colonoscopy findings are summarized in Table 1. On multivariate analysis, independent predictors for PCCRC included adenoma with high-grade dysplasia (OR: 6.35 [95% CI: 3.13-12.86], p<0.0001) and age ≥50 years [Table 2].

Conclusion
Our findings from a large nationwide database in the United States show similar rates of post-colonoscopy colorectal cancer after positive FIT as compared to large population-based studies from Europe. In addition, our findings reinforce the shorter colonoscopy surveillance intervals for individuals found to have adenoma with high-grade dysplasia.