"With results of this groundbreaking study, we now can safely avoid chemotherapy in about 70 percent of patients who are diagnosed with the most common form of breast cancer", said co-author Kathy Albain, an oncologist at Loyola Medicine in a Chicago suburb.
However, new work published in the New England Journal of Medicine and announced at the American Society of Clinical Oncology meeting shows that for some of the most common breast cancer scenarios, doing without chemotherapy doesn't shorten life expectancy.
The life of a woman with terminal breast cancer has been saved by a pioneering new therapy, say USA researchers.
Hormone-receptor-positive, axillary node-negative disease accounts for approximately half of all cases of breast cancer in the USA, and the National Institutes of Health has previously recommended adjuvant chemotherapy for most patients, the authors write.
The research, involving a genetic test is already available on the NHS and has revealed less than a third of women with the most common form of the disease benefit from the treatment.
Thousands of women have been tested over the years using Oncotype DX to help determine the true effectiveness of chemo.
The woman has been cancer-free for two years, reported the US -based team, presenting their results as "a new immunotherapy approach" for the treatment of patients with a late-stage form of the disease.
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Cancer doctors said the findings would change practice in United Kingdom clinics, and meant women in this group could be treated safely with just surgery and hormone therapy.
Previous clinical trials using immunotherapy to treat breast cancer have proved largely ineffective. Those who score 26 or higher on the scale do benefit and now receive chemotherapy. We have known that for a long time. It took place over the last ten years and followed over ten thousand women.
The study enrolled 10,273 women, of whom 9719 with follow-up data were included in the main analysis set; 6711 women (69%) had an intermediate recurrence score of 11-25, while 1619 (17%) had a low recurrence sore of 10 or less and 1389 (14%) had a recurrence score of 26 or higher.
Doctors who cared for the woman at the US National Cancer Institute in Maryland said Perkins's response had been "remarkable": the therapy wiped out cancer cells so effectively that she has now been free of the disease for two years.
He added: "This is an extraordinary day for breast cancer doctors and for women who have breast cancer". They benefit just as much from chemotherapy, which many don't tolerate well and can have long-term consequences, as they do from hormone treatments, which have many fewer side effects. Your odds of being cured are terrific, and you don't need chemotherapy because you don't need it. "Nothing magical happens" at the point where a low score becomes intermediate or intermediate becomes high risk, she cautioned. In addition to their Oncotype DX results, women most likely to be able to skip chemo have breast cancer that has not spread to their lymph nodes and have tumors smaller than five centimeters in diameter.
"What that test does is look at 21 different genes to see if each is turned on or off and then if it is over-expressed or not", Brawley said. Survival was similar in both groups, with over 9 in 10 women still alive 9 years after treatment.
This resulted in a "highly personalized" anti-cancer therapy that yielded "complete tumor regression", the researchers wrote. "There are some people who say, 'I don't care what you say, I'm never going to do chemo, '" and won't even have the gene test, she said.