Combining immunotherapy and radiotherapy helps the immune system hunt down and destroy cancer cells not killed by the initial radiotherapy, a study says.

Treating cancers with immunotherapy and radiotherapy at the same time could stop them becoming resistant to treatment, according to research.

Scientists found combining the two treatments helped the immune system hunt down and destroy cancer cells that were not killed by the initial radiotherapy in mice with breast, skin and bowel cancers, the study published in Cancer Research found.

Radiotherapy is a very successful treatment for many forms of cancer, but in cancer cells it does not kill it can switch on a "flag" on their surface, called PD-L1, that tricks the body's defences into thinking they pose no threat.

The immunotherapy works by blocking these "flags" to reveal the true identity of cancer cells, allowing the immune system to see them for what they are and destroy them.

The approach improved survival and protected the mice against the disease returning.

"Using the body's own defences to treat cancers has huge potential with early phase clinical trials demonstrating exciting patient benefit, but we are still at the early stages of understanding how best to use these types of treatments," Dr Simon Dovedi, the lead researcher based at the University of Manchester and member of the Manchester Cancer Research Centre, said.

"Combining certain immunotherapies with radiotherapy could make them even more effective and we're now looking to test this in clinical trial to see just how much of a difference it could make."

The researchers were based at the university and funded by MedImmune, the global biologics research and development arm of AstraZeneca, and Cancer Research UK.

Professor Nic Jones, Cancer Research UK's chief clinician, says around half of all cancer patients are given radiotherapy and it has been at the heart of helping improve survival rates so that today one in two cancer patients will survive for at least 10 years.

"Doctors and researchers are constantly looking for ways to improve treatments and this approach could open the door to a whole new way of giving radiotherapy," Prof Jones said.

Dr Robert Wilkinson, director of oncology research at MedImmune, says it is committed to developing strong science-led collaborations and supporting research that helps further advance scientific understanding in the important area of immunotherapy.

"The findings described in the recent study with Cancer Research UK are extremely encouraging," Dr Wilkinson said.

Cancer Research UK joined forces with The Christie NHS Foundation Trust and the University of Manchester to form the Manchester Cancer Research Centre, allowing doctors and scientists to work closely together.

Copyright AAP 2014.