A woman with advanced breast cancer has been "cured" by an injection harvested from her own immune system in what scientists have described as an "extremely promising" world first.
Judy Perkins, a 52-year-old mother of two, was given months to live after seven types of chemotherapy failed and she had developed tumours the size of fists in her liver.
She had undergone a mastectomy in 2003 after the cancer was first diagnosed, but it returned in 2013 and spread aggressively.
There is no known cure for breast cancer patients whose disease has spread so widely.
But Ms Perkins, an engineer from Florida, has now been completely cancer free for two years and leads an active life including 40-mile hikes and kayaking.
Using a technique called adoptive cell transfer, scientists removed a tumour from her chest and determined which friendly T cells within it were capable of recognising the harmful cancer cells.
Over eight weeks, the team at the National Cancer Institute harvested the T cells into an army of 82 billion and then injected them back into Ms Perkins, turbocharging her immune system against the cancer.
The method has previously been used with mixed success on patients with bowel, cervical and liver cancers, but this is the first time it has been tried on someone with breast cancer.
Experts believe the case, discussed at the American Society of Clinical Oncology meeting in Chicago, marks the start of a breakthrough for thousands of women who currently have no hope.
The Institute of Cancer Research said: "This fascinating and exciting study in a single breast cancer patient provides a major 'proof-of-principle' step forward, in showing how the power of the immune system can be harnessed to attack even the most difficult-to-treat cancer."
The treatment identified 23 per cent of Ms Perkins's T cells were useful for attacking the genetic mutations specific to her cancer.
The team targeted four out of her 62 mutations and after a year all the tumours had completely disappeared.
"I was very sceptical about whether this treatment would work because I knew the odds were not really great," said Ms Perkins.
"But within two weeks I could feel the tumours in my chest wall shrinking and I started to feel better.
"It feels miraculous and I am beyond amazed that I have now been free of cancer for two years.
"Experts may call it extended remission but I call it a cure."
By the time the new trial started, the cancer had spread to her liver, as well as lymph nodes in her chest wall and abdomen.
Dr Steven Rosenberg, a leading member the medical team, said: "This patient came to us in a desperate situation, with every treatment having failed.
"The breakthrough here is in finding an approach able to identify the T cells which target genetic mutations and in being able to grow them to this number.
"But the important point is that this is using a patient's own cells to attack their own cancer."
There are typically more than 55,000 new cases of breast cancer diagnosed in the UK each year, while around 11,500 people die from the disease.
Immunotherapies, such as adoptive cell transfer, are playing an increasingly prominent role in the treatment, however currently only about 20 per cent of patients respond.
Dr Simon Vincent, director of the British charity Breast Cancer Now, described the trial, which is published in Nature Medicine, as "remarkable and extremely promising", but said it should be repeated in other patients before giving hope of a cure for metastatic breast cancer.
He added: "It's also highly significant that this outcome suggests reprogramming patients' immune cells as part of a two-pronged attack could be a viable way to treat ER-positive tumours – which could open this approach up to benefit many patients with metastatic breast cancer."