Hallmarks of Cancer 8: Evading Immune Destruction
The eighth and final Hallmark of Cancer is the cell’s ability to evade destruction by the body’s immune system. There are three phases to this process: elimination, equilibrium, and escape. Normally, the body’s immune system searches for abnormal and damaged cells and destroys them before they can develop into cancers and tumors. T cells of the immune system are able to target specific cells and kill them.
If the cancerous cells are able to avoid elimination, they exist in an equilibrium phase that balances cell growth and immune suppression. Basically, the cancer cells are not allowed to proliferate uncontrollably, but they cannot be completely removed by the immune system either. Research suggests that during this equilibrium phase, the cancer cells are able to develop adaptations and learn how to evade the immune system. Finally, if the cancer cells are able to adapt to the immune system, they can escape any form of immune suppression. Often times, cancer cells will be able to interfere with checkpoint pathways of the immune system so that they cannot be killed.
An example of this Hallmark of Cancer can be seen with melanoma, a type of skin cancer. These cancer cells are able to avoid being eliminated by the body’s immune system. During the equilibrium phase, some cancer cells undergo genetic changes due to the immune system and are held dormant while other cancer cells are able to adapt to the immune system. These cells then go on and grow into a tumor. Research suggests that immunotherapies could be a possible effective form of treatment. Combination therapies that target multiple pathways also seem to be the most effective. It is important to note that the immune system is not ignorant of cancerous cells, but is rather suppressed by them. Studies are focusing on how to remove suppression of the immune system. 1
1 Mittal, D. Gubin, M.M., Schreiber, R.D., Smyth M.J. New Insights into Cancer Immunoediting and its Three Component Phases – Elimination, Equilibrium, and Escape. Current Opinion in Immunology. 2014;27:16-25. April 2014.