SARS-CoV-2-Induced Gut Microbiome Dysbiosis: Implications for Colorectal Cancer

Simple Summary Specific guidance regarding cancer treatment in coronavirus disease-19 (COVID-19) patients is lacking due to minimal knowledge. It has been observed that patients with severe COVID-19 develop a dysbiotic microbiota of the gut. This impact may be long-lasting, resulting in a greater possibility of a future diagnosis of colorectal cancer (CRC) or aggravating the condition in those already afflicted. Given that CRC is the third most common and third deadliest type of cancer, we must understand how infection with SARS-CoV-2 will impact CRC biology and treatment strategies. The emergence of a novel coronavirus, severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), in December 2019 led to a worldwide pandemic with over 170 million confirmed infections and over 3.5 million deaths (as of May 2021). Early studies have shown higher mortality rates from SARS-CoV-2 infection in cancer patients than individuals without cancer. Herein, we review the evidence that the gut microbiota plays a crucial role in health and has been linked to the development of colorectal cancer (CRC). Investigations have shown that SARS-CoV-2 infection causes changes to the gut microbiota, including an overall decline in microbial diversity, enrichment of opportunistic pathogens such as Fusobacterium nucleatum bacteremia, and depletion of beneficial commensals, such as the butyrate-producing bacteria. Further, these changes lead to increased colonic inflammation, which leads to gut barrier disruption, expression of genes governing CRC tumorigenesis, and tumor immunosuppression, thus further exacerbating CRC progression. Additionally, a long-lasting impact of SARS-CoV-2 on gut dysbiosis might result in a greater possibility of new CRC diagnosis or aggravating the condition in those already afflicted. Herein, we review the evidence relating to the current understanding of how infection with SARS-CoV-2 impacts the gut microbiota and the effects this will have on CRC carcinogenesis and progression.