Contrary to what was previously believed, the immune system’s cancer-killing T cells are more effective in a tumor’s anoxic environment when they have access to growth factor VEGF-A. Researchers now show how the T cells not only survive in this oxygen-depleted micro-environment with the help of transcription factor HIF-1a but also become more effective at killing cancer cells inside it.

https://www.sciencedaily.com/releases/2017/11/171113123616.htm