Cancer is the leading cause of death world-wide and is characterized by the uncontrolled growth of abnormal cells whose ability to evade the human body’s immune system is a significant factor in their proliferation and persistence.
The immune system is the body’s natural defence system. It is a collection of organs, cells and special molecules that help protect against infections, cancers and other diseases. When a foreign organism enters the body, the immune system recognises it and attacks it, preventing it from causing harm. Cancer cells are abnormal cells and trigger an immune response in the same manner as any other foreign organism.
Generally speaking, cancer develops in three phases:
- Elimination. The body’s immune system identifies targets and destroys cancer cells as they develop and before they can form tumours that threaten a person’s health.
- Equilibrium. The body has identified and destroyed some cancer cells, but others are less visible to the immune system and remain.
- Escape. Those cancer cells that have evaded the immune system because they are less visible start to multiply and form tumours. As this stage the body is unable to control further development and spread of the tumour by itself.
A significant contributing factor to the development of cancer beyond the elimination phase is the ability of some kinds of cancer cells to evade detection by the immune system. Some tumours express a protein called PD-1 that binds to receptors in the surface of T-cells preventing them from recognising a cancer cell as dangerous. Disruption of PD-1 and the subsequent ability of T-cells to recognise and target cancer cells is one focus of immune-oncology.
Immunotherapy is a comparatively recent class of cancer treatment that seeks to harness the innate powers of the immune system to fight cancer. It works to enhance the body’s natural response to an invasive foreign body and for this reason it may hold greater potential than traditional therapies to fight cancer more powerfully, to offer longer-term protection against the disease, to cause fewer side effects, and to benefit more patients with more cancer types.