The Enteric Microbiome in Early-Onset Colorectal Cancer: A Comprehensive Review of Its Role as a Biomarker of Disease

Early-onset colorectal cancer (EoCRC), a distinct entity from late-onset colorectal cancer (LoCRC), continues to increase in incidence. Known risk factors for LoCRC have been explored to explain this trend, but do not account for it completely. The gastrointestinal microbiome has been associated with LoCRC and additional risk factors of disease; however, it is only now being investigated in the context of EoCRC. A better understanding of the microbiome's function in EoCRC could elucidate its role in the increasing incidence of EoCRC. This article reviews the state of literature related to studies specifically isolating microbiome-related changes in EoCRC compared with LoCRC and age-matched controls. Several studies reviewed in this article highlight the varied results of overall diversity and specific bacteria that are influenced by EoCRC, and the utility of these unique changes to predict for EoCRC. Although the microbiome can be useful in understanding EoCRC, to better predict for disease the microbiome must be studied in more diverse populations and with deeper, more functional characterization in a manner that allows for transference of findings among future studies. These studies indicate that the enteric microbiome holds significant potential as a biomarker for disease but has yet to fully meet an understanding necessary for direct clinical utilization.