Microplastics and Human Cancer Risk: A Comprehensive Review of Environmental, Molecular, and Nanotoxicological Perspectives.

Microplastics (MPs) are plastic particles measuring less than 5mm that form when larger plastic items gradually degrade. These widespread environmental pollutants are increasingly regarded as potential threats to human health because of their distinctive physicochemical characteristics, which may promote interactions with biological systems involved in carcinogenesis. Growing experimental evidence indicates that some MPs can facilitate cellular internalization and traverse biological barriers. In vitro and preclinical research further suggests that MPs may modulate molecular pathways implicated in cancer progression and multidrug resistance (MDR), though direct clinical data remain scarce. Mechanistic studies indicate that MPs can trigger oxidative stress, persistent inflammation, epithelial-mesenchymal transition, endocrine disturbances, DNA damage, and alterations in immune function, potentially supporting tumour initiation and progression. MPs may also function as "Trojan horses" by carrying environmental contaminants, intensifying their toxic and carcinogenic effects. Furthermore, nanoscale particles can affect signalling pathways relevant to glioblastoma development, despite no direct evidence currently demonstrating that long-term environmental exposure initiates or accelerates glioblastoma in humans. This review critically evaluates the available mechanistic and toxicological evidence concerning the possible involvement of MPs in carcinogenesis, treatment resistance, immune dysregulation, and neurotoxicity. It highlights key knowledge gaps, the need for standardized detection methods, and considers possible mitigation and regulatory measures. Overall, current findings support the biological plausibility that chronic MP exposure could influence carcinogenic processes. However, evidence establishing a causal association remains inadequate, and well-designed mechanistic, epidemiological, and longitudinal investigations are needed to guide evidence-based policies.