2022 ASCO Annual Meeting: Using Biomarker Testing to Avoid Radiation Therapy in People 55+ With Luminal A Breast Cancer

2022 ASCO Annual Meeting; #ASCO22
June 7, 2022
Brielle Gregory Collins, ASCO staff

The theme of the 2022 American Society of Clinical Oncology (ASCO) Annual Meeting is Advancing Equitable Cancer Care Through Innovation. From June 3 to 7 in Chicago, Illinois, and online, cancer researchers and clinicians from around the world will gather to discuss the latest research and how to ensure that all people receive the cancer care they need.

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Some of the notable research that will be presented today includes: 

Biomarker testing may help people 55+ with low-grade luminal A breast cancer avoid radiation therapy after surgery

Who does this study affect? People aged 55 or older with low-grade luminal A breast cancer who have received breast-conserving surgery.

What did this study find? The phase 3 LUMINA clinical trial found that radiation therapy may not be needed for patients aged 55 or older who have received breast-conserving surgery for low-grade luminal A breast cancer, as identified through biomarker testing.

Luminal A breast cancer is hormone receptor-positive, HER2-negative cancer that has low levels of the protein Ki-67, which can indicate how quickly cancer cells are growing. Ki-67 is a type of biomarker, which is a substance created by cancer cells in the body. Biomarkers are identified using a tool called biomarker testing, or tumor marker testing, which can help doctors recommend treatment.

People with a low grade, or slow-growing, type of luminal A breast cancer typically receive breast-conserving surgery (also called lumpectomy) to remove the tumor followed by hormone therapy and radiation therapy to reduce the risk of the recurrence, which is the chance of the cancer coming back. However, if radiation therapy can safely be avoided, that means patients won’t have additional side effects and costs of the treatment. Because people with luminal A breast cancer are known to have a low risk of recurrence, the researchers in this study were evaluating whether some people with this cancer could avoid radiation therapy after surgery without it impacting their risk of recurrence.

This study included 500 women aged 55 or older with low-grade luminal A breast cancer. Participants had received biomarker testing to confirm that 13.25% or less of their cancer cells had Ki-67. All participants had a grade 1 or 2 tumor smaller than 2 centimeters (about ¾ of an inch) that had been removed with breast-conserving surgery and no cancer in the lymph nodes. The median age of the participants was 67, and 88% of the participants were younger than 75. The median is the midpoint, meaning half of the participants were older than 67 and half were younger.

Participants in the study then received hormone therapy for 5 years after surgery but did not receive radiation therapy. They had a check-up every 6 months for the first 2 years and then once a year after that.

At a median follow-up of 5 years, the recurrence rate, or percentage of participants who had their cancer come back, was very low at 2.3%. The study also found that the breast cancer came back in the opposite breast from where it started in 1.9% of participants, and the percentage of participants whose cancer had not come back was 97.3%. And, 89.9% of participants had no signs of cancer at 5 years and 97.2% were still alive at the time of follow-up.

What does this mean for patients? People aged 55 or older with low-grade luminal A breast cancer, as identified through biomarker testing, may be able to safely avoid radiation therapy after breast-conserving surgery without impacting their risk of recurrence.

"Previous studies have shown that other tumor biomarkers can identify patients at very low risk of recurrence, thereby omitting chemotherapy as it is unlikely to offer benefit. The LUMINA results show that women with low levels of the Ki67 biomarker can avoid outcomes related to radiotherapy, including significant acute and late side effects; such effects include fatigue and rare life-threatening side effects of cardiac disease and second cancers.”

— lead study author Timothy Joseph Whelan, MD, FASCO
McMaster University and the Juravinski Cancer Centre
 Ontario, Canada

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