Microplastics and Colorectal Cancer: Presence in Human Colorectal Tissues and Associations with Tumor Biology- A Systematic Review

Background Colorectal cancer (CRC) is recognized as one of the major health issues affecting the world, whose incidence and mortality are increasing. Nowadays, environmental pollutants, such as microplastics (MPs), have become a possible factor in colorectal carcinogenesis. The small plastic particles (< 5 mm) are known as MPs that do not disappear, and therefore they may accumulate in the human tissues, posing concerns about their role in tumor biology. Objective To conduct a systematic assessment of the existence of microplastics in human colorectal mucous membranes and their interconnections with the markers of tumor nature and biological pathways in CRC. Methods A systematic review was performed according to Preferred Reporting Items of Systematic Reviews and Meta-Analyses (PRISMA). MEDLINE, EMBASE, Web of Science, and Cochrane library were identified as sources of peer-reviewed studies published in January 2019-December 2025. The inclusion criteria were that the studies needed to analyze MPs in human colorectal tumor or adjacent tissues and that they also analyzed relationships with tumor biology, such as pathological, inflammatory, or molecular markers. Two reviewers were individually involved in screening, selection, and data extraction. The final qualitative synthesis comprises 13 studies, having undergone title/abstract and full text screenings. Some of the extracted data were study design, sample size, type of tissue, methods of detecting MP, polymer type, size of the particle, and the tumor biological outcomes. Results MPs were accurately identified in colorectal tissues and the concentration in tumor tissues exceeded that in adjacent or control tissues. The most common polymers, which were primarily less than 100 µm in size, were poly-ethylene, poly-propylene and poly-styrene. The increased MP burdens were linked to the advanced tumor stage, low differentiation, increased levels of the pro-inflammatory cytokines, evidences of oxidative stress, disturbed immune infiltration, and disturbed epithelial barrier function. Mechanistic research indicates that MPs have the ability to establish an oxidative stress induction, inflammatory, and immune homeostasis with the potential to generate a pro-tumorigenic microenvironment. Conclusion MPs exist in the human colorectal tissues and are clustered in tumors preferentially, which may have an impact on the progression of CRC. Multicenter studies with conventional application are required to specify causal mechanisms and clinical implications.