A potentially, revolutionary therapy that trains the immune system to attack cancer has shown what US-based scientists have described as extraordinary results in early trials involving terminally ill patients.

In the most promising early human trial, 35 patients with acute lymphoblastic leukaemia underwent the treatment.

94% experienced complete remission, meaning their symptoms disappeared.

Patients with other blood cancers saw response rates greater than 80%, with more than half experiencing complete remission.

However, scientists have warned much more work is required before it could become a viable treatment.

The technique involves removing immune cells from patients, tagging them as the kind of molecules that target cancer, and putting them back in the body.

Once there, they reduce the chances of the cancer being able to shield itself from the immune system.

Seattle-based Professor Stanley Riddell, who led the yet to be peer-reviewed study, said it was unprecedented to get such response rates in patients with such advanced cancer.

However, he added much work still needed to be done, as it was not clear how long-symptom free patients would remain in remission.

Some trial participants also suffered a relapse during treatment and seven suffered a serious side effect caused by an over-powerful immune response, with two dying.