Immune system can halt tumour growth
US-based research has suggested that the immune system may be able to stop a tumour from growing, even though the cancer is not actually eliminated.
The findings, which have been described as "the newest milestone" in our understanding of how the immune system reacts against cancer, suggest that it may be possible to use the immune system to contain cancer by sending the tumour into a dormant state.
Researchers injected genetically modified mice with small doses of a cancer-causing chemical and noticed that while some of the mice developed tumours, others developed smaller growths that only became full-blown tumours if certain parts of the animals' immune systems were disabled.
Publishing their findings in the journal Nature, the researchers suggest that the mice's immune systems had previously been holding their tumours in check, a state described as "equilibrium" in which the immune system reduces cancer cells' ability to replicate and kills some of the cancer cells, although not enough to destroy the tumour.
Dr Robert Schreiber, professor of pathology and immunology at the Washington University School of Medicine, commented: "Thanks to the animal model we have developed, scientists can now reproduce this condition of tumour dormancy in the laboratory and look directly at cancer cells being held in check by the immune system. That will allow us to see if we can model this state therapeutically."
The researchers suggest that many people may harbour dormant tumours that are in a state of equilibrium with the immune system. These tumours may either develop spontaneously as we age, or because of exposure to cancer-causing chemicals.
However, they believe that the human immune system has not evolved to deal effectively with cancer.
Dr Schreiber explained: "Cancer is typically a disease of the elderly, who have moved beyond their reproductive years, so there probably was no evolutionary pressure for the immune system to find a way to fight cancer."
The researchers now intend to investigate what happens in tumours and the immune system at a molecular level during equilibrium, and to test their results in humans and on different types of cancer.
Co-author Dr Mark Smyth, professor of the Cancer Immunology Programme at the Peter McCallum Cancer Centre in Melbourne, said: "We may one day be able to use immunotherapy to artificially induce equilibrium and convert cancer into a chronic but controllable disease.
"Further research and clinical validation of this process may also turn established cancers into a chronic condition, similar to other serious diseases that are controlled long-term by taking a medicine."
Dr Lesley Walker, director of cancer information at Cancer Research UK, said: "Tumour dormancy is where patients may suffer a recurrence of their cancer many years later and it is a well-recognised clinical phenomenon that is poorly understood.
"Clearly there would be enormous benefits to be gained if we could develop therapies that stopped these cells from growing. These researchers have provided us with some insights into how the immune systems of mice may operate to keep potentially malignant cells in check."