Pairing chemo and immunotherapy can deliver a double-whammy punch that knocks out deadly drug-resistant breast cancer, new research has shown.
Scientists who tested the approach on mice found that animals remained cancer-free even after they were given new tumours, indicating long-lasting immune protection.
Unlike some other cancers, including those of the lung and skin, breast cancer is not known to respond well to treatments that harness the immune system.
But a remarkable transformation was seen when an international team of scientists combined targeted chemotherapy with antibody-based immunotherapy.
Tumours lost their ability to shield themselves from the immune system, allowing immune cells to attack the cancer.
Writing in the journal Science Translational Medicine, researchers led by Dr Philipp Muller, from the University of Basel in Switzerland, described the results as "striking".
An extremely treatment-resistant cancer had been transformed into tumours that were "highly vulnerable to immune attack".
The scientists added: "Ultimately, this resulted in complete cures in our pre-clinical model."
The "target" cancer used in the study was a form known as Her2 positive, which affects between 15% and 20% of women with breast cancer.
Patients with this disease are genetically programmed to over-produce the cancer-driving Her2 protein.
In most cases, patients develop resistance to Her2 targeted treatments such as the drug Herceptin.
The new research involved combining a cancer-destroying chemotherapy drug with certain antibodies, including those that prevent cancer escaping detection by the immune system.
This resulted in immune cells, such as cancer-fighting T-cells, converging on the tumours.
Surprisingly, it also attracted "regulatory T-cells" whose normal job is to tone-down immune responses. Removing the regulatory T-cells resulted in the mice developing severe autoimmune disease, demonstrating their crucial role in preventing "collateral damage" during immunotherapy.
Jackie Harris, clinical nurse specialist at the charity Breast Cancer Care, said: "This is a very interesting early study carried out on mice that shows the future possibility of providing alternative options when a patient becomes resistant to existing drugs.
"Her2 positive breast cancer can be difficult to treat.
"So bringing together different treatment methods that help us to ensure each patient receives the very best medical care appropriate for them is a welcome step forward.
"The more we know about the disease, the more we can develop better treatments.
"We look forward to seeing the results of further clinical trials."