Cancer that comes back after treatment could be reawakened by the body’s immune system, research suggests.
The study found that normally beneficial immune system signals can be subverted by surviving cancer cells.
Instead of helping to fight cancer, they then promote its relapse and growth.
Immunotherapy treatments that target this response were shown in mice to delay or prevent cancer returning.
Professor Alan Melcher, from the Institute of Cancer Research, London, said: “Our study finds the body’s own immune system seems to play a crucial role when cancer relapses.
“The immune system goes from keeping cancer cells in check to awakening and feeding residual cells, while turning a blind eye to their growth.
“Excitingly, many of the methods employed by treatment-resistant tumours to regrow and hide from the immune system can be blocked using existing immunotherapies.
“This idea is, in fact, supported by emerging data from clinical trials, showing that immunotherapies can reduce the risk of cancers coming back.”
Resistant cancer cells were found to have large numbers of a molecule called PD-L1 on their surfaces, which helped shield them from attack by immune system T-cells.
The molecule interacts with the molecular “receptor” PD-1, the target for new immunotherapy drugs called “checkpoint inhibitors”.
Co-author Professor Kevin Harrington, also from the Institute of Cancer Research, said: “It is becoming increasingly clear that the immune system is at the core of the puzzle of how we can treat cancer more effectively.
“This fascinating new study helps explain why sometimes a patient’s immune system can be effective against cancer cells while at other times it is not. It also shows there is a lot more to learn about the nature of those cancer cells that lie dormant as a way of resisting the killing effects of cancer treatments.
“Changes must occur in these cells that make them better able to manipulate the immune system – and understanding this could open up new treatment options to prevent relapse.”
The findings are reported in the journal Cancer Immunology Research.
