Fig. 2

The 3 E’s of tumor immunoediting: tumor formation occurs through accumulation of mutations induced by various stress factors like radiation, virus, chemicals and other carcinogens. During initial tumor growth, the tumor cells undergo dynamic interactions with the immune system, which is called tumor immunoediting and can be divided into 3 distinct phases. I. Elimination In this phase the balance is tilted towards the immune system. Large numbers of CD8⁺, CD4⁺ T cells along with NK-cells, macrophages and dendritic cells mount an effective response to the tumor. Soluble factors like IFNγ, perforin, granzyme lead to tumor cell apoptosis and elimination of cancer. II. Equilibrium In this phase an equilibrium exists between the tumor and immune system. The immune system tries to shift the balance towards elimination whereas the tumor cells also apply mechanisms to avoid immunesurveillance. III. Escape The continuous assault by the immune system may lead to development of tumor cells that are less immunogenic and can avoid the immune system. The tumor has several strategies to escape the immune system; these include induction of T cell apoptosis, blocking dendritic cell maturation and promoting generation of immunosuppressive Treg cells. Hence the balance shifts towards the tumor and tumor development can occur unhindered