Histopathological characteristics of screen-detected colorectal cancers

Screen-detected colorectal cancers (CRCs) represent an increasing proportion of diagnoses as population screening is expanded. They are associated with improved prognosis compared to non-screening cases even when adjusted for stage. We aimed to evaluate the histopathological features and impact on survival of faecal immunochemical test (FIT)-based screen-detected CRCs with comparison to a cohort of non-screening cases. We analysed a database of screen-detected CRCs (n = 191) in our institution since screening began in 2012 with comparison to a cohort of non-screening cases (2019-2020, n = 358). Histopathological reports were reviewed for prognostic factors such as lymphovascular invasion (LVI), perineural invasion (PNI) and tumour budding. The patient record was reviewed for survival analysis. Screen-detected CRCs were associated with an earlier stage of diagnosis (p = 0.002) and had lower rates of serosal involvement (T4) (20% vs 33%, p = 0.001), PNI (7% vs 16%, p = 0.002) and extramural venous invasion (EMVI) (11% vs 29%, p < 0.0001). Screen-detected rectal cancers also had higher complete response rates to neoadjuvant therapy (42% vs 17%, p = 0.024). Overall survival was superior in screening cases (χ² = 13.58, p = 0.0002). Multivariate survival analysis showed that mode of detection (screening versus non-screening), lymphatic invasion, PNI and stage were independently associated with improved survival. In conclusion, screen-detected CRCs have distinct characteristics that are associated with improved overall survival. They are diagnosed at an earlier stage and have a more favourable risk profile with lower rates of PNI, EMVI and serosal involvement (T4). The response to neoadjuvant therapy is also superior to non-screening cases. These factors may contribute to the well-documented improved prognosis of screen-detected CRCs.