Some older women with luminal A breast cancer can safely forgo radiotherapy, study shows
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CHICAGO — Patients aged 55 years or older with low-grade luminal A breast cancer who receive endocrine therapy can safely avoid radiotherapy after breast-conserving surgery, according to a prospective study presented at ASCO Annual Meeting.
“We estimate that these results could apply to as many as 30,000 to 40,000 women per year who could avoid the morbidity, inconvenience and cost of radiotherapy,” Timothy Joseph Whelan, MD, FASCO, professor of oncology and Canada research chair in breast cancer research at McMaster University, said during a presentation.
Background and methods
Adjuvant radiotherapy is common after breast-conserving surgery and has been associated with a 67% reduction in risk for local recurrence, Whelan said. However, the daily treatments for up to 5 weeks can be inconvenient and costly for patients, and can result in significant acute and late toxicity, as well as rare life-threatening adverse effects.
As risk for local recurrence has decreased and surgical techniques and systemic therapies have improved, Whelan and colleagues sought to determine whether biomarker screening results could be used to identify patients with very low-risk disease for whom adjuvant radiotherapy could be omitted.
The single-arm, phase 3 LUMINA study included 500 patients aged 55 years or older (mean age, 67 years; mean tumor size, 1.1 cm) with node-negative breast cancer and luminal-A type tumors, defined as ER of 1% or greater, PR greater than 20%, HER2-negative and Ki67 of 13.25% or less. The Ki67 protein has been associated with cancer cell proliferation.
The patients, accrued between August 2013 and July 2017 from 26 centers across Canada, underwent breast-conserving surgery and received endocrine therapy for at least 5 years.
Local recurrence served as the primary outcome. Secondary outcomes included contralateral breast cancer, as well as recurrence, DFS and OS.
Median follow-up was 5 years.
Key findings
Results showed 10 local recurrence events, all invasive, for a 5-year local recurrence rate of 2.3% (90% CI, 1.3-3.8). Researchers observed a similar 5-year rate of contralateral breast cancer (1.9%; 90% CI, 1.1-3.2; n = 8) and a 2.7% (90% CI, 1.6-4.1) rate of any recurrence (n = 12). Whelan reported a 5-year DFS rate of 89.9% (90% CI, 87.5-92.2) and 5-year OS rate of 97.2% (90% CI, 95.5-98.4). Only one patient died due to breast cancer.
Implications
“Women aged 55 years or older with T1N0, grade 1 to grade 2 luminal A breast cancer following breast-conserving surgery treated with endocrine therapy alone had a very low rate of local recurrence at 5 years,” Whelan said. “The prospective and controlled nature of this multicenter study supports that such patients are candidates for omission of radiotherapy.”
Perspective
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Deborah M. Axelrod, MD
More than two-thirds of all breast cancers are luminal A cancers. They are ER- and PR-positive and HER2-negative and have low levels of the protein Ki67, which reflects cell growth. In this study, women had luminal A cancers with Ki67 of 13%, which is considered on the lower side, and negative lymph nodes. They are the most favorable of the invasive cancers.
In the last decade, we have acquired more knowledge about the behavior of breast cancers based on molecular subtyping. Results of studies such as this have given us information on cancers that need more treatment and cancers for which we can de-escalate treatment. Refining this more, it’s about reducing morbidity and improving quality of life without compromising the oncologic outcome.
The big strength of this study is that it is prospective and many centers participated. It has been supported by other studies, as well, and will define the patients with newly treated breast cancers for whom can we omit radiation, which has been the standard of care. These findings confirm the results of the PRIME II study, as well.
The study has several limitations, including the fact that it is a single-arm study with no radiation therapy comparison arm and it involved older patients with smaller tumors. Local recurrence for ER-positive cancers continues to rise after 5 years, so longer term follow up will be important. In addition, some older patients may prefer radiation therapy — especially accelerated partial breast irradiation of a week — to 5 years of endocrine therapy, which was mandated in this study.
The omission of radiation therapy should be considered an option for older women with localized breast cancer with favorable features who receive endocrine therapies. At NYU, our radiation oncology department participates in trials that stratify breast cancer beyond their clinical and pathologic features, such as the PRECISION trial, in which we use a genomic assay called the PAM50 (Prosgina, Veracyte) and the DEBRA trial, which uses the Oncotype DX assay (Exact Sciences).
NYU Langone Health
Perspective
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Kamran Ahmed, MD
LUMINA is an important clinical trial that examined the role of omission of radiotherapy in low risk, early-stage breast cancer. It followed the results of PRIME II and CALGB 9343, looking specifically at patients with luminal A disease.
The 5-year data presented at ASCO showed a low risk for recurrence with adjuvant endocrine therapy alone. As we wait for further data maturation, it is important to note that not all patients with early-stage breast cancer are the same and for patients to have a tailored discussion with their radiation oncologist regarding their unique risk-benefit ratio in determining their radiation treatment plan.
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Whelan TJ, et al. Abstract LBA501. Presented at: ASCO Annual Meeting; June 3-7, 2022; Chicago.
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