"We can spare thousands and thousands of women from getting toxic treatment that really wouldn't benefit them", said Dr Ingrid A Mayer, from Vanderbilt University Medical Center, an author of the study.
Results from a major study could change the lives of tens of thousands of women with breast cancer.
The majority of women with early stage breast cancer who are treated with chemotherapy do not need it, according to a major global study. Most women in this situation don't need treatment beyond surgery and hormone therapy, he said. Some study leaders consult for breast cancer drugmakers or for the company that makes the gene test. A high recurrence score, above 25, means chemo is necessary to ward off a recurrence while a low score, below 10, means it is not.
These were divided into groups that will receive chemotherapy followed by hormonal therapy or hormonal therapy alone.
Arnie Purushotham, a senior clinical adviser to Cancer Research UK who was not involved in the study, welcomed the TAILORx results as an important step toward making cancer treatment less harsh for patients.
After enrolling for new trial in 2015, doctors in the USA adopted an experimental approach combining two different forms of immunotherapy after conventional hormone treatments and chemotherapy failed.
For women 50 or younger, chemotherapy is unwarranted for those with an Oncotype score under 16 - about 40 percent of breast cancers in this age group, the researchers said.
'Now with these genomic tests, we are finding that we have multiple types of breast cancer, perhaps several dozen and we are being able to tailor our therapies to the type of breast cancer every woman has, ' Brawley added.
In a very different type of immunotherapy called CAR-T therapy, a patient's T-cells, the warriors of the immune system, are removed, and then genetically re-engineered in a lab to better recognize the patient's own cancer.
A new class of patients could soon be treated for breast cancer, no chemotherapy required.
Women with a score above 25 generally are given chemotherapy.
That could affect up to 70,000 women a year in the United States of America and thousands more around the world, the study said.
According to the TAILORx researchers, 260,000 women who are diagnosed with breast cancer each year around the world fall into the medium-risk category that wouldn't benefit from chemotherapy.
Previous research has shown that women with a low Oncotype Dx recurrence score (less than 10) are likely to respond to hormone therapy alone, whereas those with a score above 26 benefit from having a combination of chemotherapy and hormone therapy.
The outcome was extraordinary, leading to "complete durable regression" of the rapidly spreading cancer that was growing in the patient's liver.
Jacoub told Healthline it's the women with mid-range scores of between 11 and 25 that have provided oncologists with tough decisions.
Litton, the MD Anderson oncologist, said doctors need to consider each case on its own merits and cautioned against ruling out chemo too quickly.
Dr. Jennifer Litton at MD Anderson Cancer Center in Houston, agreed, but said: "Risk to one person is not the same thing as risk to another". It was uncertain whether the benefits of chemotherapy were enough to justify the risks and toxicity.
"I have definitely hit the jackpot", said Judy Perkins. By finding, isolating and multiplying the tiny subset of immune cells that are still in the fight, then demonstrating their ability to vanquish a patient's tumors, Rosenberg's group has shown that "the cells are there", Mackall said. There is still a long way to go, he said, but it's an approach that isn't specific to a certain cancer type, meaning it could evolve into an effective therapy for many forms of the disease, he said.