Figure 2. The 3 E's of Cancer Immunoediting.

The concept of cancer immunoediting during the course of tumor development consists of three phases Elimination, Equilibrium and Escape. Elimination: during the early phase of tumorigenesis, when tumors are microscopic, the immune system eliminates the highly immunogenic cells leaving the poorly immunogenic ones behind. Equilibrium: as the immunogenic cells are eliminated, tumors enter an equilibrium (or dormant) phase where the immune system prevents tumor growth. Escape: changes in the tumor cells or stroma within the microenvironment can facilitate uncontrolled tumor growth and metastasis. Shown on the right are representative photos of melanoma bearing Grm1 (Glutamate metabotropic receptor) transgenic mice, where tumors regress when mice are treated with immunotherapy (top). Both melanoma cells and melanocytes are eliminated as shown by the absence of tumor and depigmentation of the fur. Histology staining (H and E) of paraffin sections of ear shows no tumor burden with residual melanin. In some instances, tumors are non-responsive to immunotherapy and continue to progress (bottom). Histology staining of these ears show heavy tumor burden.