"We all don't need cookie cutter medicine for things", said 20-year breast cancer survivor Alesa Garner.
It will spare 500 to 600 women in Ireland having chemotherapy annually.
Women at low risk could skip chemo.
Dr Harold Burnstein, from the American Society of Clinical Oncology, said: "This study will transform care immediately, and for the better". After years of follow-up, the data showed that most patients who did not get chemotherapy fared as well as those who did.
The woman was 49 when she signed up for the clinical trial after several attempts at a cure through conventional treatments had failed, said the study published in the scientific journal Nature Medicine.
The study is based on the test, Oncotype DX, which examines 21 genes from a patient's biopsy sample to determine how active they are.
Testing solved a big problem of figuring out who needs chemo, said Dr. Harold Burstein of the Dana-Farber Cancer Institute in Boston. This is one more piece of information that will help form treatment plans, along with information like the patient's health history, her exact type of cancer, her stage of cancer, and her age. Patients with scores between 11 and 25, though, represent an uncertainty.
Across the European Union, we have seen positive results for breast cancer care as more women are being diagnosed and treated earlier, leading to higher survival rates. But it can fail, often because it cannot recognise cancer cells containing the patient's own DNA.
Women with a score above 25 generally are given chemotherapy.
The breast cancer study focused on cases where chemo's value increasingly is in doubt: women with early-stage disease that has not spread to lymph nodes, is hormone-positive (meaning its growth is fueled by estrogen or progesterone) and is not the type that the drug Herceptin targets.
The majority of women with the most common type of early-stage breast cancer can safely skip chemotherapy after surgery, according to a highly anticipated new report. This left a lot of women, an estimated 65,000 in the US each year, in a gray zone, unsure if they would benefit from chemo.
According to first author Joseph Sparano of Montefiore Medical Center in NY, "any woman with early-stage breast cancer 75 or younger should have the test and discuss the results" with her doctor. Longer-term effects of chemotherapy include infertility and heart failure.
But in a discussion of the results, Dr Lisa Carey, from the University of North Carolina in the U.S., drew attention to some of the subtle differences between the groups.
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. That doctors and researchers need to constantly re-evaluate the assumptions on which medical decisions are based, especially for something as important and time-sensitive as cancer treatments. Those at high risk are advised to receive it but intermediate was a toss-up until this study.
Where did these results come from?The results were presented at the annual cancer conference (ASCO) held in Chicago.
Albain is excited to share the study results with her clients in her practice. "If confirmed in a larger study, it promises to further extend the reach of this T-cell therapy to a broader spectrum of cancers".