Cancer is the failure of the immune system to detect and destroy abnormal growths in the body. Macrophages, here genetically tagged in yellow, identify and destroy abnormal cells. T cells are much more specific, recognizing and responding to single antigen. Cancers have some how managed to subvert both of these defenses. In this image both the red T-cells and yellow macrophages have infiltrated the tumor, but have become stuck and ineffectual, allowing it to grow.