After nine years, 94 percent of the women in both groups were still alive.
A leading oncologist said the findings will lead to a "fundamental change" in how the disease is treated.
A promising experimental treatment has left a Florida woman's advanced breast cancer in remission.
"This is a hard call when you are actually the one with the breast cancer", an early-stage breast cancer survivor from Middleton, Massachusetts, told LifeZette.
Researchers at the National Cancer Institute (NCI) examined over 10,000 breast cancer patients and found that women who were treated with an estrogen-blocking hormone therapy had a almost identical survival rate to women treated with chemo and hormone therapy.
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.
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.
A sample of the tumour is tested after surgery for 21 genetic markers, which indicate if it could grow and spread.
Those with a recurrence score of up to 10 out of 100 have been shown not to benefit from chemo and those with a score of 26 or higher do benefit.
The study, which used genetic testing and included about 10,000 patients, revealed that women with smaller-sized, estrogen-fueled tumors that had not spread to the lymph nodes fared just as well without chemo as those who received it.
The results are expected to spare as many as 70,000 women from the expensive procedure that comes with harsh side effects.
The big outstanding question was: What should women with "midrange" scores get?
Now, the "vast majority of women who have this test performed on their tumor can be told they don't need chemotherapy, and that can be said with tremendous confidence and reassurance", Burstein stated.
"Many women with breast cancer will be able to be spared unnecessary chemotherapy", said Dr. Erna Busch-Devereaux, a breast surgeon at Northwell Health's Huntington Hospital, in Huntington, N.Y. Oncotype DX has spurred the trend, and is likely to accelerate it. Using this test, researchers found that chemotherapy did not add any benefit in survival rates or recurrence for most women.
Other less common but more serious side effects of chemotherapy include bone loss and osteoporosis, heart and vision problems. "Now we know there's no need to give chemotherapy to those patients anymore", Mitchell said. "It was all gone", she said.
Phyllis Laccetti, a 58-year-old night nurse at Montefiore, was diagnosed with cancer in her right breast in 2007.
Dr Ring said the trial's reuslts would likely have an immediate impact on United Kingdom practice and represented a significant shake-up in the treatment of early-stage breast cancer.
The study found that women over 50 scoring up to 25 did not need chemo, nor did women under 50 with a score up to 15.
"Oncologists have been getting much smarter about dialing back treatment so that it doesn't do more harm than good", said Steven Katz, a University of MI researcher who examines medical decision-making.