A combination of immunotherapy and a virus could treat aggressive breast cancer, an 'absolutely amazing' study has revealed.
Breakthrough research showed the pairing cured up to 90 per cent of mice plagued by triple negative breast cancer - deemed the deadliest form.
Canadian scientists are hopeful the findings will lead to a potential cure, as survival depends on how early the disease is caught.
The trial, led by Ottawa University scientists, comes as a separate study found that an injection of a virus could also treat aggressive brain tumours.
Breakthrough research showed the pairing cured up to 90 per cent of mice plagued by triple negative breast cancer - deemed the deadliest form
Dr Marie-Claude Bourgeois-Daigneault, lead author of the Canadian study, was full of praise for the findings, which may apply to humans.
She said: 'It was absolutely amazing to see that we could cure cancer in most of our mice, even in models that are normally very resistant to immunotherapy.
'We believe that the same mechanisms are at work in human cancers, but further research is needed to test this kind of therapy in humans.'
Every year 11,400 people die from breast cancer in the UK. In the US, the figure is around four times higher.
Charities estimate around 15 per cent of all cases of breast cancer are triple negative - but death rates are proportionally higher.
The study, published in Science Translational Medicine, adds to the growing body of evidence that shows the vast benefits of immunotherapy.
All of the mice in the study were resistant to the checkpoint inhibitor, which blocks proteins on cancer cells to stop them from growing, that was used.
IMMUNOTHERAPY: THE FACTS
Immunotherapy, described as 'game changing', is hailed as the biggest advance in cancer treatment in decades.
It is considered far kinder than chemotherapy, which can cause pain and loss of appetite by targeting healthy and diseased cells.
Instead, immunotherapy 'turbo-charges' the immune system so it targets and kills just cancer cells. It's usually given in weekly infusions.
The treatment has already proven hugely effective against some deadly cancers, extending the lives of terminal patients by up to five years.
Despite the array of research, the drugs were rejected for NHS funding in April before health chiefs back tracked in the autumn.
They vowed in September to fund the drug denied to Sunday Times food critic AA Gill - which he called the weapon of choice for 'every oncologist in the first world'.
This type of drug - made famous by nivolumab, which Sunday Times food critic referred to as the weapon of choice for 'every oncologist in the first world' before he died, is already used to treat some forms of cancers, including lung and kidney.
Separate trials showed an oncolytic virus called Maraba boosted the immune system of the mice, attacking the cancerous cells.
However, it had little effect on their survival of mice on its own. The rodents were engineered to be in a state of metastasis - when the cancer has spread from the original location.
When it was used alongside the checkpoint inhibitor it cured between 60 and 90 per cent of the mice.
This was compared to a 0 per cent cure rate for the immunotherapy alone and 20 to 30 per cent for just a dose of the virus.
The new treatment, which backs up older trials using the same technique, saw the virus given before surgery and the drug after.
Dr John Bell, co-author, added: 'Our immune system is constantly trying to recognize and kill cancer cells, but the cancer cells are always trying to hide from it.
'When you infect a cancer cell with a virus, it raises a big red flag, which helps the immune system recognize and attack the cancer.
'But in some kinds of cancer this still isn't enough.
'We found that when you add a checkpoint inhibitor after the virus, this releases all the alarms and the immune system sends in the full army against the cancer.'
Researchers recently confirmed oncolytic viruses and checkpoint inhibitors have potential for treating melanoma.
The new study was the first to test viruses and checkpoint inhibitors in a surgery and metastasis model, which is particularly relevant for patients.
THE VIRUS THAT COULD TREAT PEOPLE WITH BRAIN TUMOURS
A virus injected directly into the bloodstream could be used to treat people with aggressive brain tumours, a separate study found.
Scientists discovered reovirus could cross the blood-brain barrier to reach tumours, where it replicates and kills the cancer cells.
They also found the virus was able to 'switch-on' the body's own defence systems to attack the cancer - like immunotherapy.
British researchers believe reovirus therapy could be used alongside chemotherapy or immunotherapy to make treatment more potent.
The only side effects reported in the study, which involved nine patients, were flu-like symptoms. Further trials are underway.
The findings, by researchers at Leeds University and The Institute of Cancer Research in London, were published in Science Translational Medicine.