The two groups, taken together, account for about 70 percent of women diagnosed with the most common type of breast cancer.
A leading oncologist said the findings will lead to a "fundamental change" in how the disease is treated.
Each year more than 20,000 women in the United Kingdom are diagnosed with hormone-receptor positive, HER2-negative, node-negative breast cancer.
In the nine years of the study, 93.9 percent of the patients only using hormone therapy survived breast cancer.
What can you say about this latest development in breast cancer treatment study?
The study was supported by the National Cancer Institute, the American College of Surgeons, Cancer and Leukemia Group B, NSABP Foundation, NCIC Clinical Trials Group, North Central Cancer Treatment Group, and Southwest Oncology Group.
The breast cancer epicemic can not be reversed without considering women's exposure to chemical cocktails throughout their lives, argued Professor Andreas Kortenkamp of the University of London, presenting new scientific evidence to the European Parliament. Following this "recalibration" of the genetic test, the researchers estimated that chemotherapy was not justified in 70% of cases of breast cancer.
The 21-gene recurrence-score Oncotype Dx assay is one of several commercially available gene expression assays that can offer prognostic insight in hormone-receptor-positive breast cancer.
Patients with a recurrence score of up to 10 out of 100 have been shown not to benefit from chemotherapy and only hormone treatment is required.
Announcement imminent as Manchester United schedule medical for next week
But he told the magazine: "I am not close at all". "I think being the coach of a club is my job. Mourinho had previously claimed that he would like to coach his country, when he feels "tired".
The patients then went on to receive either hormonal therapy alone or the combo of hormonal therapy plus chemotherapy.
The results are even more impressive because breast cancers, like prostate and ovarian cancers, have relatively few mutations - which makes it much harder for the immune system to differentiate and attack them.
"We can spare thousands and thousands of women from getting toxic treatment that really wouldn't benefit them", Dr. Ingrid A. Mayer, from Vanderbilt University Medical Center and author of the study, was quoted as saying.
Those women should carefully discuss their options with their oncologist, said Brawley, because they would likely be candidates for the more aggressive, dual therapies.
This means thousands of women will be able to avoid all of the side effects chemotherapy implies, such as nausea, vomiting, hair loss and fatigue, while still achieving positive long-term outcomes. The prospective TAILORx study was created to help to discover whether chemotherapy is beneficial for women with a mid-range recurrence score of 11 to 25, as well as to prospectively confirm that a low recurrence score of 0-10 is associated with a low rate of distant recurrence if patients receive endocrine therapy without adjuvant chemotherapy.
More specifically, in women over 50 years (whose risk of recurrence is lower), chemotherapy is useless for a score between 0 and 25. Doctors do say chemotherapy is still effective and necessary in treating certain patients.
The 52-year-old mother-of-two from Florida has been disease-free for nearly two years. Longer-term effects of chemotherapy include infertility and heart failure. Patients using both types of treatment had an overall survival rate of 93.8 percent.
There was some benefit from the chemotherapy for a small subgroup - women with a score of 16 to 25 who were age 50 or younger, Sparano's team said. Clearly communicating research findings are important for helping patients make informed decisions about treatment and modifying risk.