medwireNews: Radiotherapy may not be necessary for patients with the luminal A breast cancer intrinsic subtype and a low clinical risk for recurrence, the LUMINA investigators reported at the 2022 ASCO Annual Meeting in Chicago, Illinois, USA.
Presenting author Timothy Whelan, from McMaster University in Hamilton, Ontario, Canada, said that the study findings “could apply to as many as 30,000 to 40,000 women per year” in North America, allowing these patients to avoid the “morbidity, inconvenience, and cost of radiotherapy.”
He explained that the study is based on findings from the Toronto-BC trial indicating that patients with the luminal A breast cancer subtype based on immunohistochemistry and a low clinical risk had the smallest risk for recurrence after breast-conserving surgery plus adjuvant tamoxifen and did not benefit from the additional use of radiotherapy.
To investigate further, the LUMINA trial recruited women with luminal A disease, defined as estrogen receptor expression of at least 1%, progesterone receptor expression above 20%, HER2-negative status, and a Ki67 score of 13.25% or less, as determined from 500 nuclei taken from five random areas of tumor samples.
These patients were all aged 55 years or greater, and had invasive ductal T1N0, grade 1–2 disease. They had received breast-conserving surgery that achieved margins of at least 1 mm and sentinel lymph node biopsy, as well as endocrine therapy, consisting of 5 years or more of treatment with an aromatase inhibitor or tamoxifen.
The primary outcome of any invasive or noninvasive local recurrence within 5 years was assessed in 500 patients and 10 invasive events occurred, giving a cumulative 5-year rate of 2.3%. “The upper bound of the 90% confidence interval – 3.8[%] – is well below our boundary of 5.0%,” the presenter said.
The 5-year cumulative rates of contralateral breast cancer, any recurrence, and disease-free survival were 1.9%, 2.7%, and 89.9%, respectively. The overall survival rate at 5 years was 97.2%, with only one of the 13 deaths reported related to breast cancer.
“The prospective and controlled nature of this multicenter study supports that such patients are candidates for omission of radiotherapy,” Whelan concluded.
Session discussant Jennifer Bellon (Dana-Farber Cancer Institute, Boston, Massachusetts, USA) described the LUMINA study findings as “amazing” and coming “from a well-conducted and well-thought-out study.”
Considering whether omitting radiotherapy should be the standard of care for this patient population, Bellon said that even if the risk for local recurrence after 5 years is increased with the omission of radiotherapy, “it is highly unlikely that there will be any compromise in distant disease or overall survival.”
She also mused that as the risk of for distant disease in the LUMINA population may be very low, it might also be possible and preferable to omit endocrine therapy rather than radiotherapy.
The discussant concluded that “patient-reported preferences and values will be key to guiding decision-making” and that further validation is required to “solidify” the LUMINA findings.
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