Hypoxia is a common feature of solid tumors, and develops because of the rapid growth of the tumor that outstrips the oxygen supply, and impaired blood flow due to the formation of abnormal blood vessels supplying the tumor. It has been reported that tumor hypoxia can: activate angiogenesis, thereby enhancing invasiveness and risk of metastasis; increase survival of tumor, as well as suppress anti-tumor immunity and hamper the therapeutic response. Hypoxia mediates these effects by several potential mechanisms: altering gene expression, the activation of oncogenes, inactivation of suppressor genes, reducing genomic stability and clonal selection. We have reviewed the effects of hypoxia on tumor biology and the possible strategiesto manage the hypoxic tumor microenvironment (TME), highlighting the potential use of cancer stem cells in tumor treatment.

Colorectal cancer (CRC) is the third most common cause of cancer globally and the fourth attributable cause of mortality and morbidity due to cancer. An emerging factor contributing to CRC is the gut microbiota and the cellular changes associated with it. Further insights on this may help in the prevention, diagnosis and new therapeutic approaches to colorectal cancer. In most cases of CRC, genetic factors appear to contribute less to its aetiology than environmental and epigenetic factors; therefore, it may be important to investigate these environmental factors, their effects, and the mechanisms that may contribute to this cancer. The gut microbiota has recently been highlighted as a potential risk factor that may affect the structural components of the tumor microenvironment, as well as free radical and enzymatic metabolites directly, or indirectly. Many studies have reported changes in the gut microbiota of patients with colorectal cancer. What is controversial is whether the cancer is the cause or consequence of the change in the microbiota. There is strong evidence supporting both possibilities. The presence of Fusobacterium nucleatum in human colorectal specimens has been demonstrated by RNA-sequencing. F. nucleatum has been shown to express high levels of virulence factors such as FadA, Fap2 and MORN2 proteins. Our review of the published data suggest that F. nucleatum may be a prognostic biomarker of CRC risk, and hence raises the potential of antibiotic treatment of F. nucleatum for the prevention of CRC.

Exosome-encapsulated microRNAs are being suggested as a new class novel biomarker and diagnostic and predictive markers in colorectal cancer. These particles are released from many cell types into the extracellular space upon fusion of multivesicular bodies (MVB) with the plasma membrane. They contain a wide variety of information, including proteins, lipids, RNAs, non-transcribed RNAs, microRNAs, which can be circulated in various body fluids (e.g., blood, salvia, ascites, urine). Exosomes can be taken up by neighboring or distant cells and thereby modulate the functional of recipient cells and play a key role in disease progression or facilitate metastasis in cancers. The aim of current review is to give an overview about origin and trafficking of exosomes between cells, techniques to isolate exosomal microRNAs as well as the potential applications of exosome-encapsulated microRNAs as diagnostic markers in clinical settings in colorectal cancer. There is growing body of evidence showing the prognostic and diagnostic value of some exosomal microRNAs in colon cancer (e.g., miR-150, miR-21, miR-192, let-7a, miR-223, and miR-23a). These findings provide a new insight on novel application of these markers as being novel non-invasive biomarkers for early detection and risk assessment of patients with colorectal cancer, although further investigations in larger population are required to explore the clinical utility of exosomal microRNAs in colorectal cancer patients.