Some patients with early-stage, low-risk breast cancer may not need radiation therapy after breast conserving surgery, according to new research from the UBC faculty of medicine, BC Cancer, McMaster University and Hamilton Heath Sciences.
The study, 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.
With the new approach, a significant proportion of patients can be spared of radiation after breast conserving surgery, allowing them to avoid the harmful side effects and adding capacity back into the public health care system to increase access for those who need it most.
“This is a major advance in our treatment approach for breast cancer. With a better understanding of the molecular biology of breast cancer we can now identify women who do not need radiation,” said Dr. Tim Whelan, lead author of the study, professor of oncology at McMaster University and a radiation oncologist at Hamilton Health Sciences.
Dr. Torsten Nielsen
Typically, people with early stage breast cancer receive daily radiation treatment for several weeks after breast conserving surgery to reduce the risk of cancer returning. However, radiation can be costly, inconvenient for the patient and cause both short-term side effects — such as tiredness and skin irritation — and long-term side effects — such as breast pain and thickening of the breast tissue, which can affect how the breast looks and a patient’s quality of life.
The subtype of breast cancer that researchers focused on, called luminal A, represents up to 60 per cent of all breast cancers diagnosed annually. The study followed 500 women from across Canada who were 55 years of age or older, had undergone breast conserving surgery, and had tumours that were smaller than two centimetres without cancer in the lymph nodes under the arm.
The growth rate of a patient’s tumour was assessed with a simple, low-cost and made-in-B.C. version of a molecular test called Ki67. If determined to be low risk, patients were enrolled in the trial where they received standard endocrine therapy but not radiation.
At five years post-surgery, the 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.
“Adding the simple and affordable Ki67 test allows us to identify patients who can avoid the inconvenience and side effects of breast radiation.”
Dr. Sally Smith
“I want to thank all the women who had the courage to sign up for this study. 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,” said Dr. Torsten Nielsen, professor of pathology and laboratory medicine at UBC and clinician-scientist at BC Cancer. Nielsen developed the version of the Ki67 molecular test used in this clinical trial.
“The Ki67 test uses an inexpensive and easy method called immunohistochemistry, and can replace more costly and complicated testing methods. Ki67 uses an antibody applied to tissues and a simple chemical reaction to identify how fast tumours are growing. The test is affordable, open source and can be made available at hospital labs around the world,” said Nielsen.
Radiation therapy is standard practice, so trial 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.
Dr. Sally Smith
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.
“We are increasingly able to individualize care for patients with cancer. Adding the simple and affordable Ki67 test allows us to identify patients who can avoid the inconvenience and side effects of breast radiation. This, indirectly, helps to ensure resources are directed to patients who benefit from radiation therapy,” said Dr. Sally Smith, clinical assistant professor of surgery at UBC and a radiation oncologist at BC Cancer – Victoria. Dr. Smith was the Western Canada Regional lead for the study.
The study’s findings were initially presented in June 2022 at the American Society of Clinical Oncology (ASCO) Annual Meeting in Chicago and have since been peer-reviewed and are now being published in full detail.
The hypothesis for the publication was based on findings from a previous BC-Toronto study that found radiotherapy can reduce local recurrence of breast cancer, and that patients with favourable clinical features have a low risk. In an effort to further classify patient risk of recurrence who might avoid radiotherapy, and with support from Canadian Institutes of Health Research (CIHR), a translational study published in 2015 utilized the Ki67 molecular marker to identify a low-risk group of luminal A breast cancer patients. These findings came from a retrospective analysis and required clinical validation, leading to the current publication indicating that they can potentially be spared of radiotherapy.
The study received funding from the Canadian Cancer Society and the Canadian Breast Cancer Foundation.