Oxygen deprivation in breast cancer: mechanisms, pathways, and implications.

Hypoxia, a state of reduced oxygen availability, is a defining feature of the tumor microenvironment in breast cancer. It arises from the rapid proliferation of cancer cells, which outpaces the development of adequate vasculature. This oxygen deprivation triggers a cascade of molecular and cellular adaptations that enable tumor cells to survive and thrive under hostile conditions. Key among these is the stabilization of hypoxia-inducible factors, which regulate genes involved in angiogenesis, metabolic reprogramming, immune evasion, and cell survival. Hypoxia significantly influences breast cancer behavior, promoting tumor aggressiveness, therapeutic resistance, and metastatic potential. The hypoxic microenvironment fosters angiogenesis through vascular endothelial growth factor signaling, albeit leading to abnormal and inefficient vasculature. It also reprograms cancer cell metabolism towards glycolysis, supporting survival and growth in oxygen-deprived regions. Furthermore, hypoxia modulates immune responses, suppressing anti-tumor immunity while promoting the recruitment of immunosuppressive cells. These multifaceted effects underscore hypoxia's pivotal role in shaping the clinical trajectory of breast cancer.