A potentially revolutionary therapy that trains the immune system to attack cancer has shown "extraordinary" results in early trials involving terminally ill patients.
In one study 94 per cent of participants with acute lymphoblastic leukaemia (ALL) saw their symptoms vanish completely.
Patients with other blood cancers saw response rates greater than 80 per cent with more than half experiencing complete remission.
The technique involves removing immune cells called T-cells from patients, tagging them "receptor" molecules that target cancer, and infusing them back in the body.
Scientists screened specially bred genetically engineered mice for the targeting molecules, known as chimeric antigen receptors or Cars.
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Once attached to the T-cells, they reduce the chances of the cancer being able to shield itself from the immune system.
Lead scientist Professor Stanley Riddell, from the Fred Hutchinson Cancer Research Center in Seattle, US, said the results were extraordinary.
"These are in patients that have failed everything. Most of the patients in our trial would be projected to have two to five months to live," Riddell said.
"This is extraordinary. This is unprecedented in medicine to be honest, to get response rates in this range in these very advanced patients."
"These are in patients that have failed everything. Most of the patients in our trial would be projected to have two to five months to live."
Riddell, who was speaking at the American Association for the Advancement of Science (AAAS) annual meeting in Washington DC, described the results as a "potential paradigm shift" in cancer treatment.
At the same time he acknowledged that much more work had to be done, and it was not clear how long the symptom-free patients would remain in remission.
So far, the technique has only been tried on patients with "liquid" blood cancers.
Riddell hopes to progress to patients with solid tumours, but points out that this will be challenging.
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Although the immune system is geared to combat cancer, very often it fails in the task.
Cancer cells are not recognised by the body's defences, or find ingenious ways to mask their identity.
In other research reported at the meeting, scientists made progress tracking T-cells with long memories as part of a new approach to combating cancer.
Immune cells with long memories allow some vaccines to provide life-long protection against viruses or bacteria.
An Italian team led by Professor Chiara Bonini, from the University of Milan, found a way to track T-cells with a memory of cancer for up to 14 years.
The findings imply that the right immunotherapy might act as a vaccine, providing long-term protection against cancer.
