Exploring disparities in adherence to colorectal cancer clinical practice guidelines and associated survival outcomes: a systematic review and meta-analysis.

Colorectal cancer (CRC) remains a major global health burden, where adherence to evidence-based guidelines is critical for improving patient outcomes. This systematic review aimed at synthesising the effects of structural and systemic barriers on CRC clinical practice guidelines (CPGs) recommendations, adherence, and treatment outcomes, drawing on real-world evidence. This systematic review followed Preferred Reporting Items for Systematic Reviews and Meta-Analyses and was registered with PROSPERO (CRD42024621251). Literature was searched in Scopus, Web of Science, MEDLINE, CINAHL, and Cochrane from inception to 26 May 2026. Eligible studies included cohort and observational studies comparing CRC patients managed according to CPG adherence versus non-adherence recommendations. Primary outcomes were adherence rates and overall survival. Pooled analyses were conducted using a random-effects model. Of 4,262 initially identified citations, 95 met the inclusion criteria, and 30 were included in the meta-analysis. Adherence shows heterogeneous, tumour-stage-specific associations with survival, though effects varied by tumour site, disease stage, and treatment modality. Non-adherence was more common among patients of advancing age and those facing structural disadvantage, including socioeconomic strata, non-white ethnicity, and treatment in non-accredited facilities. Across all tumour sites, adherence to CPGs was associated with a non-significant survival benefit [Risk Ratio (RR) = 0.90; 95% confidence interval (CI = 0.67-1.20; heterogeneity I2= 99.78%]. Subgroup analysis by tumour-stage recommendation demonstrated significant survival advantages for Stage II (RR = 0.58; 95% CI 0.34-0.99; I2 = 97.59%) and Stage III colon cancer (RR = 0.58; 95% CI 0.41-0.80; I2 = 97.11%). In contrast, adherence to Stage II-III rectal cancer recommendations showed only a non-significant trend toward improved survival (RR = 0.59; 95% CI 0.34-1.03; I2 = 35.53%). Disparities in guideline adherence reflect structural and systemic disparities in cancer care delivery. These findings underscore the need to address barriers that contribute to non-adherence, particularly among identified high-risk populations and within the health-care system, to support more equitable guideline-adherent care.