A new treatment for breast cancer has completely eradicated tumours in just 11 days, doctors have announced.
Describing the unexpected results as "staggering", they added that they had never seen breast cancer patients respond so quickly to a cancer treatment.
The UK team, announcing the results at the European Breast Cancer Conference in Amsterdam, said the new two-pronged technique could spare thousands of women gruelling chemotherapy.
Those who were newly diagnosed with an aggressive form of breast cancer were given the therapy at 23 UK hospitals.
A total of 87 per cent of the participants in the trial responded to the treatment, with tests showing the cancer had stopped producing more cells.
But for some women, the results were more dramatic. In 11 per cent, the tumours had completely vanished, to the surprise of surgeons, and for another 17 per cent they had significantly shrunk.
Doctors combined two existing cancer drugs - Tyverb and Herceptin - and gave them to women as soon as they were diagnosed. The team, led by the University of Manchester and the Institute of Cancer Research in London, had initially aimed simply to shrink tumours in the days before women were to have surgery.
But when surgeons tried to remove lumps that had measured up to 3cm wide just a few days earlier, they found that in some women the tumours had vanished.
Professor Nigel Bundred, a cancer surgeon in Manchester who led the study, said: "For solid tumours to disappear in 11 days is unheard of. These are mind-boggling results."
Professor David Cameron, an oncologist at Edinburgh University, said: "It was only when the pathologists were scratching around in the lab saying 'Where is the tumour?' that it became apparent there was no tumour at all."
The experts said that because the trial was relatively small - involving 257 women, of whom 66 took the combination treatment - further tests are needed before they consider making it more widely available.
"These results are so staggering that we will have to run another trial to prove they are generalisable," said Professor Bundred.
"But it is clear what has happened: we are pretty certain that we are not only getting tumour disappearance, we are getting an immune response as well."
The treatment was given to women with the HER2-positive form of breast cancer, which affects around 8,000 in Britain every year.
Herceptin, which is delivered via a drip, is often used alongside chemotherapy to treat those with this form of the disease, but usually only after surgery in an attempt to stop the cancer returning.
Tyverb, which is also known as Lapatinib, is a pill used by women with advanced breast cancer, usually when other treatments have failed and the disease has spread to other parts of the body.
By giving the combination at the very beginning, as soon as a woman was diagnosed, the researchers found they could eradicate the disease rapidly.
Women will still have to have surgery to make sure no cancer cells are left, but the doctors hope it will mean they do not have to have chemotherapy afterwards.
In combination, the drugs cost just under £1,500 for an 11-day course, and because Tyverb is nearing the end of its patent the cost is expected to plummet.
Professor Bundred said: "A large chunk of evolution is not about suddenly finding a new drug - it is about finding a new way to use the drugs we already have in a new way."
Cancer charities welcomed the findings last night and called for more research so patients can share the benefits as soon as possible.
Samia al Qadhi, chief executive at Breast Cancer Care, said: "Although an early study, this has game-changing potential."
Baroness Delyth Morgan, chief executive at Breast Cancer Now, added: "We hope this particularly impressive combination trial will serve as a stepping stone to an era of more personalised treatment for HER2-positive breast cancer.
"Such a rapid response before surgery could soon give doctors the unprecedented ability to identify women responding so well to combined HER2-targeting drugs that they would not need gruelling chemotherapy.
"We'll now need to see the results replicated in larger trials and to understand how such a positive response to combined HER2- targeted drugs before surgery - and the avoidance of chemotherapy - could impact on survival."
Professor Arnie Purushotham, of Cancer Research UK, which funded the study, said:
"These results are very promising if they stand up in the long run and could be the starting step of finding a new way to treat HER2-positive breast cancers.
"This could mean some women can avoid chemotherapy after their surgery, sparing them the side-effects and giving them a better quality of life."
TWO POWERFUL DRUGS, ONE PURPOSE: HOW IT WORKS
HER2-positive tumours are more deadly because of the HER2 (human epidermal growth factor) proteins on the surface of normal breast cells, which accelerate the growth of cancers.
A decade ago Herceptin, the first gene-targeted "wonder drug", boosted patients' five-year survival rates from 66 per cent to 95 per cent when it was given to them after surgery, alongside chemotherapy.
The new treatment combines Herceptin with another powerful drug called Tyverb and is given to women in the days after they are diagnosed.
Herceptin, given via a drip, latches on to the surface of cancer cells, attacking them from the outside by stopping the HER2 protein working.
Tyverb is given as a pill, working inside the cancer cells and blocking the HER2 signals that make the cells grow.
MALE SUFFERERS "GET WRONG TREATMENT"
Men with breast cancer are at a disadvantage and may be dying because they are treated in the same way as women, experts have warned.
Nearly 400 men are diagnosed with the disease each year in the UK and doctors have until now assumed the cancers are the same. But analysis of 1,500 male breast cancer patients from nine countries found key differences between their tumours and those of women.
The project, led by the Erasmus Medical Centre in Rotterdam, revealed that male breast cancers have different connective tissue, different cells, and are affected by the immune system in a different way. The discovery means that until now men may not have been treated in the best way.
Speaking at the European Breast Cancer Conference in Amsterdam yesterday, pathologist Dr Carolien van Deurzen said the results of the study could lead to "better treatment choices" for male breast cancer patients in future.
Baroness Delyth Morgan, chief executive at Breast Cancer Now, said: "This study... could change how decisions about the necessity of chemotherapy for certain male patients are made."
- Daily Mail