May 12, 2015 — Women with luminal A subtype breast cancer, particularly those over 60, may not need radiation treatment if they are already taking hormone therapy, according to a new study from the Princess Margaret Cancer Centre. The research is published in the Journal of Clinical Oncology.
The findings potentially advance delivery of personalized cancer medicine for up to 25 percent of women diagnosed with breast cancer in North America every year, said co-principal investigators Fei-Fei Liu, M.D., chief, radiation medicine, and Anthony Fyles, M.D., staff radiation oncologist. Liu is chair of the Department of Radiation Oncology at the University of Toronto, where Fyles is also a professor. In Ontario alone, they estimate, this could save the provincial healthcare system up to $3 million annually.
They stress, however: "For all other breast cancer subtypes, radiation therapy is definitely of benefit and the required treatment."
Liu and Fyles examined tumor specimens from participants in a prior randomized clinical trial who received either tamoxifen (hormone therapy) plus whole-breast radiation therapy, or only tamoxifen.
The research team analyzed molecular biomarkers in these samples, which were then classified into six subtypes. The results demonstrated that women in the luminal A subtype had the best outcome, with a 10-year risk for local relapse of 8 percent with tamoxifen alone versus 4.5 percent with both tamoxifen and radiation.
The relapse rate was even lower for luminal A patients older than 60 — 4.3 percent with tamoxifen alone, versus 6 percent with tamoxifen plus radiation.
"For luminal A women over 60, local breast radiation did not add benefit to their outcome," said Liu.
Luminal A is defined as ER-positive, PR-positive, HER2-negative and low Ki-67 (an indicator that breast cancer cells are slowly growing, dividing or proliferating).
Three years ago, based on these findings — which Liu presented at the American Association for Cancer Research annual meeting — the researchers recommended that a larger prospective clinical study was needed as the next step to validate that routine testing for Ki-67 should take place. That study is now under way.
"This prospective clinical study, under the auspices of the Ontario Clinical Oncology Group, is enrolling 500 participants over three years from 15 cancer centres across Canada," said Fyles, who is principal investigator for the trial.
"Post-menopausal women aged 55 or older with luminal A subtype breast cancer who are interested in participating should ask their treating physician if they are eligible for this study."
For more information: www.theprincessmargaret.ca
February 18, 2026 
