Oxygen gradients in tumor tissues implications for breast cancer metastasis - a narrative review.

Oxygen gradients within tumor tissues play a pivotal role in breast cancer metastasis, influencing critical biological processes that contribute to disease progression. Tumors often develop regions of hypoxia due to rapid growth and insufficient blood supply, which drives adaptation mechanisms that promote metastatic behavior. These low-oxygen areas trigger the activation of hypoxia-inducible factors (HIFs), which regulate genes involved in angiogenesis, epithelial-to-mesenchymal transition (EMT), and immune evasion. Such processes increase the capacity of cancer cells to migrate, invade distant organs, and survive under harsh conditions, contributing significantly to metastasis in breast cancer. The interaction between oxygen gradients and the tumor microenvironment (TME) is complex, with hypoxia inducing significant alterations in immune responses. Hypoxic regions of tumors often foster an immunosuppressive microenvironment by recruiting regulatory immune cells that inhibit the function of cytotoxic T cells and natural killer cells. This immune evasion not only allows the tumor to grow but also facilitates the spread of cancer cells to secondary sites. Furthermore, hypoxia-induced angiogenesis provides the necessary vasculature for metastatic cells to enter the bloodstream and seed distant organs, further enhancing the metastatic potential of breast cancer.