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Head and shoulders photo of Dr. Tim Whelan
HHS radiation oncologist Dr. Tim Whelan is lead author on a study that found that some women with early-stage, low-risk breast cancer may not need radiotherapy after breast conserving surgery.
July 3, 2024

Canadian researchers find radiation not necessary for patients with low-risk breast cancer

HHS radiation oncologist Dr. Tim Whelan is the study’s lead author

Some women with early-stage, low-risk breast cancer may not need radiotherapy after breast conserving surgery, according to new research led by Hamilton Health Sciences, McMaster University, BC Cancer, and the University of British Columbia.

The research, published in The New England Journal of Medicine, shows women 55 or older with a specific subtype of Stage 1 breast cancer can be effectively treated with just surgery and endocrine therapy.

The findings, which were initially presented in June 2022 at the American Society of Clinical Oncology (ASCO) Annual Meeting in Chicago, have since been peer-reviewed for publication in full detail.

“This is a major advance in our treatment approach for breast cancer.”

Women with early breast cancer who have breast conserving surgery typically receive radiation to the breast daily for several weeks to reduce the risk of cancer returning. However, radiation can be costly, inconvenient for the patient and associated with both short-term side effects such as tiredness and skin irritation; and long-term side effects like breast pain and thickening of the breast tissue, which can affect how the breast looks and a woman’s quality of life.

The subtype of breast cancer that researchers focused on – luminal A – represents up to 60 per cent of all breast cancers diagnosed annually and is associated with a lower risk of recurrence. With this new approach, a significant proportion of women can be spared of radiation after breast conserving surgery. Eliminating the need for this group to receive radiation will allow women to avoid the side effects of therapy and can add capacity back into the public health care system, permitting increased access for those who require radiation therapy more urgently.

“This is a major advance in our treatment approach for breast cancer,” says Dr. Tim Whelan, lead author of the study and a radiation oncologist at Hamilton Health Sciences (HHS). Whelan is also a professor in the Department of Oncology at McMaster University and the Canada Research Chair in Breast Cancer Research. “With a better understanding of the molecular biology of breast cancer we can now identify women who do not need radiation,” he adds.

The study was coordinated by the Ontario Clinical Oncology Group at HHS, and followed 500 women from across Canada who were 55 years of age or older, had undergone breast conserving surgery, and their tumors were smaller than two centimetres without cancer in the lymph nodes under the arm. The growth rate of a woman’s tumor was assessed with a simple, low-cost and made-in-B.C. version of a molecular test called Ki67, which provided a quantitative measure that the participant’s cancer was low-risk.

“I want to thank all the women who had the courage to sign up for this study.”

In the trial, the luminal A sub-type was determined by a low reading on the Ki67 test plus the tumor having both the estrogen and progesterone receptors. If determined to be low risk, women were enrolled in the trial where they received standard endocrine therapy but not radiation. Radiation therapy is standard practice, so participants were monitored through regular clinical exams and annual mammograms. When planning the study, the investigators predicted that the risk of developing recurrence in the breast would be very low at five years.

At five years post-surgery, researchers found the recurrence of cancer in the breast was only 2.3 per cent without radiotherapy. This was roughly comparable with a 1.9 per cent risk of developing a new breast cancer in the other, untreated breast.

“I want to thank all the women who had the courage to sign up for this study,” says Torsten Nielsen, clinician-scientist at BC Cancer and professor of pathology and Laboratory medicine at University of British Columbia. “Their courage has led to a chance to improve care for many other women who we now know confidently will not need to undergo radiation therapy.” Nielsen developed the version of the Ki67 molecular test used in this clinical trial.

The overall risk of cancer recurrence following breast-conserving surgery has decreased in recent years because of regular mammogram screening, improved surgical techniques and better systemic treatments, the authors say.

The study received funding from the Canadian Cancer Society and the Canadian Breast Cancer Foundation.