Faecal immunochemical test demonstrates modest decline in performance characteristics but additional prognostic...

To evaluate long-term colorectal cancer (CRC) incidence and faecal immunochemical test (FIT) performance in patients with low-risk symptoms over 5 years, and to examine factors influencing outcomes and mortality.

We followed 3501 symptomatic patients who underwent FIT in primary care (October-December 2019) across 225 practices in England. Building on our 18-month study, patients were tracked for 5 years using primary and secondary care records to identify new cancers and deaths.

Ten additional CRCs were diagnosed during extended follow-up (18-60 months), beyond the 45 identified in the first 18 months. Seven of these had initial negative FIT results. FIT sensitivity at ≥10 μg/g fell from 94.1% at 18 months to 80.0% (95% CI 67.0-89.6%) at 5 years, while specificity was 80.8% (95% CI 79.4-82.1%). The positive predictive value was 6.2% (95% CI 5.4-7.2%) and the negative predictive value 99.6% (95% CI 99.3-99.8%). Patients with negative FITs experienced a significantly longer time to CRC diagnosis than those with positive FITs (median 28 vs 1 month, HR 16.4, p < 0.001). Positive FITs were also linked to higher overall cancer risk (HR 1.63, p = 0.0076) and greater 5-year mortality (24.9% vs 11.9%, HR 2.8, p < 0.001).

FIT performance decreases over longer follow-up, with 12.7% of CRCs detected after initially negative results. Positive FITs were associated with increased mortality and overall cancer risk. These findings highlight the importance of robust safety-netting strategies for patients with negative FIT results.