Role of Hypoxia in Cancer Progression and Its Significance

Cancer is one of the leading causes of morbidity and mortality worldwide. While the pathophysiology of the cancer is varied, one of the central themes in the pathophysiology of cancer and its progression is hypoxia which arises from the tumor's rapid growth outpacing its blood supply leading to metabolic reprogramming and abnormal angiogenesis. Hypoxia, a situation where there is not enough oxygen for optimal survival, triggers a cascade of cellular and molecular adaptations that enable these tumorous cells to survive under the hypoxic conditions. Hypoxia, a hallmark of cancer, has significant effects on tumor growth, metastasis, and resistance to the therapeutic modalities available. In solid tumors, hypoxic zones are created due to the rapid proliferation of cancer cells outstripping their blood supply. The resultant heterogeneous oxygen delivery within the tumor leads to the generation of a hypoxic environment. Hypoxia exerts its effect via mediators, most notably hypoxia-inducible factors (HIFs).Tumor cells adapt to the hypoxic environment by various mechanisms, the switch to glycolytic metabolism, enhanced glucose uptake, and reliance on anaerobic processes of metabolism being some of them. Additionally, alterations are made to the lipid and protein metabolism to adapt to the hypoxic environment. Moreover, hypoxia also affects the tumor's immune microenvironment. Hypoxia protects the tumor by promoting immune evasion by increasing PD-L1 expression, suppressing T-cell function, and promoting the recruitment of immunosuppressive cells like myeloid-derived suppressor cells and tumor-associated macrophages. This promotes evasion from tumor surveillance and creates a hostile environment for therapeutic interventions. The implications of hypoxia extend to the therapeutic modalities available. Understanding the relationship between hypoxia and cancer biology is crucial for developing effective strategies to combat the problem that is at hand. Hypoxic conditions favor the selection of more aggressive cancer stem cells, further complicating the treatment outcomes. Targeting hypoxia and its downstream effects holds promise for improving cancer treatment.