After nine years, 94 percent of both groups were still alive - and about 84 percent were alive without signs of cancer, indicating that the chemo made no difference.
The immunotherapy treatment remains experimental and still requires considerably more testing before it can be used more widely. Her cancer did not respond to any treatments, including chemotherapy and hormone therapy, until this one- time treatment with more personalized immunotherapy.
The study looked at over 10,000 women with one specific type of breast cancer known as hormone-receptor-positive, human epidermal growth factor receptor 2 (HER2)-negative, lymph node-negative breast cancer.
Funded by the National Cancer Institute, various foundations and proceeds from the breast cancer research stamp, the study is the largest ever done on breast cancer treatment.
"Those are the cancers that have likely already metastasized and a small amount could be hiding in a woman's lung, liver or bones", said Brawley.
The TAILORx trial used the Oncotype DX test, now available on the NHS, which allows doctors to predict the likelihood of the breast cancer coming back. The gene test results are measured on a scale of 0-26.
Very high scores are at increased risk of the cancer spreading, and those patients have benefited a lot by chemotherapy.
"I will explain that's why research is so important in helping us move forward in breast cancer care that's how we will achieve a cure for breast cancer", Figueredo said.
The company now provides tests to more than 900,000 patients in more than 90 countries, Shak said.
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Commenting on the findings, Dr Harold Burstein, ASCO expert, said: "This is the most common form of breast cancer in the United States and developed countries and the most challenging decision we make with these patients is whether or not to recommend adjuvant chemotherapy with all its side effects and with its potential benefits".
All of the participants underwent surgery and hormonal therapy and half of them got chemotherapy.
The new study of almost 7,000 women found that use of the already available Oncotype DX gene test could pinpoint those women who needed chemotherapy, and those who did not.
What will she tell women who under prior guidelines received chemo and all its side effects and didn't need it after all?
In a landmark first case, Judy Perkins was diagnosed with breast cancer and given only three months to live. "Women don't have to suffer more than there is necessary to be better".
Over the years, the Cancer Institute has used its $59.8 million in proceeds for studies trying to improve early detection and to determine which cancers are most risky and need heaviest treatment and which are less so.
But, researchers say some women 50 and younger in high-risk groups might still need chemo.
"This is another significant step towards personalised breast cancer treatment and we hope these practice-changing findings will now help refine our use of chemotherapy on the NHS", she said. "Now we know there's no need to give chemotherapy to those patients anymore", Mitchell said.
"Oncologists have been getting much smarter about dialing back treatment so that it doesn't do more harm than good", Steven Katz, a University of MI researcher who examines medical decision-making, told the Washington Post.