The two faces of Blastocystis spp.: is it the cause of colorectal cancer (CRC) or a consequence of it?

Introduction Over the last few years, there has been an increase in the prevalence of Blastocystis spp. in colorectal cancer (CRC) patients. Moreover, various in vitro and in vivo studies have highlighted that intestinal colonisation of Blastocystis spp. has an influence on host immune responses leading to cellular apoptosis and membrane permeability. It has been suggested that Blastocystis spp. is an important risk factor for the worsening of CRC. Aim To present evidence concerning the association between CRC and Blastocystis spp. Material and methods A review of the literature was performed by searching Science Direct, PubMed, Scopus and Google Scholar databases up to December, 2023. Results and discussion Out of all in vitro and in vivo studies selected for this review, the majority of them have confirmed a significantly higher prevalence of Blastocystis spp. in colorectal cancer patients in comparison to the control groups. Several in vitro human colorectal carcinoma cell line studies have shown significant cytopathic and immunological effects of Blastocystis spp. Additionally, in vivo experimental animal model studies have shown that Blastocystis spp. infection significantly contributed to large intestinal polyp (colorectal adenoma) formation and the progression of colorectal carcinogenesis. Conclusions These studies strongly support suggestions that Blastocystis spp. could be an important factor to existing CRC development by influencing the host immune response and increasing oxidative damage.