What is one method by which tumors evade the immune system?

Tumors can evade the immune system through various mechanisms, and one significant method is by altering their microenvironment to suppress immune responses. This involves a range of strategies that tumors use to create a local environment that is not conducive to immune activity. For instance, tumors can release inhibitory cytokines, recruit immune-suppressive cells such as regulatory T cells and myeloid-derived suppressor cells, and modify the extracellular matrix components to prevent effective immune cell infiltration. By doing so, tumors can hinder the ability of immune cells to recognize and attack them, essentially creating a shield that protects them from immune surveillance.

In contrast, inducing cell death in neighboring tissues, avoiding growth factors, or increasing blood flow to immune cells do not directly contribute to the evasion of immune responses. While these actions may affect the tumor and its immediate environment, they do not primarily serve the purpose of suppressing the immune system's ability to target and destroy the tumor cells.