Women with luminal A subtype breast cancer, and particularly those older than 60 years, may not need radiation treatment if they are already taking hormone therapy. This clinical research was published in the Journal of Clinical Oncology (2015; doi:10.1200/JCO.2014.57.7999).

The findings potentially advance delivery of personalized cancer medicine for up to 25% of women with breast cancer in North America every year, said co-principal investigators Fei-Fei Liu, MD, FRCPC, chief, Radiation Medicine, and Anthony Fyles, MD, FRCPC, staff radiation oncologist. Both researchers are at the Princess Margaret Cancer Centre and the University of Toronto in Toronto, Ontario, Canada.

“For all other breast cancer subtypes, radiation therapy is definitely of benefit and the required treatment,” stressed the authors.

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Liu and Fyles examined tumor specimens from participants in a prior randomized clinical trial who received tamoxifen plus whole-breast radiation therapy or only tamoxifen.

The research team analyzed molecular biomarkers in these samples that 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% with tamoxifen alone versus 4.5% with both tamoxifen and radiation.

The relapse rate was even lower for luminal A patients older than 60 years: 4.3% with tamoxifen alone versus 6% 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 estrogen receptor positive, progesterone receptor positive, HER2-negative, and low Ki-67. Ki-67 is an indicator that breast cancer cells are growing, dividing, or proliferating slowly.

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 3 years from 15 cancer centers across Canada,” said Fyles, who is the principal investigator for the Princess Margaret.

“Postmenopausal women age 55 [years] 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.”

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