Biology and Clinical Implications of Fecal Occult Blood Test (FOBT) Screen-Detected Colorectal Cancer

Abstract Background Fecal occult blood test (FOBT) based screening for colorectal cancer (CRC) reduces mortality, with earlier stage at diagnosis a prominent feature. Other characteristics of FOBT screen-detected cancers and any implications for clinical management have not been well explored. Methods We examined a multi-site clinical registry to compare the characteristics and outcomes of FOBT screen-detected CRC via the Australian National Bowel Cancer Screening Program (NBCSP), which is offered biennially to 50-74 year olds, and age matched non-screen detected cases in the same registry. All statistical tests were 2-sided. Odds Ratios were calculated using the Baptista-Pike method and Hazard Ratios via the log-rank method. Results Of 7,153 registry patients diagnosed June 1, 2006 to June 30, 2020, 4142 (57.9%) were aged between 50-74 years old. Excluding 406 patients with non-NBCSP screen-detected cancers and 35 patients with unknown method of detection, 473 (12.8%) were screen-detected via the NBCSP and 3228 (87.2%) were non screen-detected. Screen-detected patients were younger (mean age= 62.4 vs 64.2 years, P<.001) and more medically fit (Odds Ratio [OR] for ASA score 1-2 = 1.91, 95% confidence interval [CI] = 1.51 to 2.41, P<.001). Pathologic characteristics within each stage favoured the screen-detected cases. Stage III screen-detected colon cancers were more likely to receive adjuvant therapy (OR = 3.58, 95% CI = 1.52 to 8.36, P=.002). Screen-detected patients had superior relapse free (HR = 0.41, 95% CI = 0.29 to 0.60, P<.001) and overall survival (HR = 0.22, 95% CI = 0.15 to 0.35, P<.001), which was maintained in matched stage comparisons and multivariate analysis. Conclusions Beyond stage at diagnosis multiple other factors associated with a favourable outcome are observed in FOBT screen-detected CRC. Given the substantial stage by stage differences in survival outcomes, if independently confirmed, individualised adjuvant therapy and surveillance strategies could be warranted for FOBT screen-detected cancers.