Epidemiological Overview of Colorectal Cancer in Kidney Transplant Recipients: A Systematic Review.

Background: Kidney transplant recipients (KTRs) experience improved survival and quality of life compared to dialysis treatment, but chronic immunosuppression may increase the risk of de novo post-transplant cancer. Colorectal cancer (CRC) is increasingly recognized in this population. This systematic review aims to synthetize contemporary evidence on CRC epidemiology, outcomes, and risk determinants among KTRs. Methods: A comprehensive search for observational and registry-based studies reporting CRC in adult KTRs was conducted on PubMed, Scopus, Web of Science, and ProQuest. The studies found were subsequently subjected to screening, data extraction, and the risk-of-bias appraisal process. Due to heterogeneity, findings were synthesized narratively. Results: Twenty-six studies encompassing 863,005 KTRs met inclusion criteria: 22 retrospective cohorts, 1 prospective cohort, 2 cross-sectional, and 1 case-control. Absolute CRC occurrence varies by geography, population, and follow-up. Reported risks ranged from no excess to modestly elevated standardized incidence ratios (SIRs): ~0.76-3.60 overall, with a right-sided colon predominance. Overall, higher mortality and worse prognosis were reported in kidney transplant recipients with colorectal cancer compared to the general population, as a result of later-stage diagnosis and more aggressive histologies. Consistent risk factors included older age, time since transplantation, diabetes and metabolic comorbidities, prior dialysis duration/graft failure, and smoking; the female sex showed higher relative CRC risk in some cohorts. The remarkable role of immunosuppression profiles was consistently highlighted: cyclosporine-azathioprine maintenance and alemtuzumab induction were associated with higher CRC risk in large registries, whereas tacrolimus-mycophenolate regimens showed lower risk signals and mTOR inhibitors suggested possible protective effects. Conclusions: Contemporary evidence suggests a modest, heterogenous increase in CRC risk among KTRs, a proximal (right-sided) predominance, and a tendency toward advanced-stage presentation with reduced survival. These findings justify the need to consider risk-tailored, lifelong surveillance strategies anchored in a full colonoscopy, with earlier initiation in younger or otherwise high-risk recipients, alongside careful optimization and periodic re-evaluation of immunosuppression. Prospective multicenter studies and cost-effectiveness analyses should refine screening thresholds and therapeutic strategies. PROSPERO ID: CRD420251071658.