Safely Omitting Breast Radiation Therapy

Breast radiation to reduce risk of local recurrence has been a standard of care for women undergoing breast conserving surgery for invasive cancer. Certain subsets of patients, including older women, have been identified who may be able to avoid radiation therapy, with no compromise in overall outcome (NEJM JW Oncol Hematol Feb 12 2023 and N Engl J Med 2023; 388:585). Another approach being explored is identifying molecular subsets of breast cancer that may not require radiation therapy in the setting of breast conservation.

The LUMINA prospective cohort study enrolled 500 women ≥55 years old with T1N0, luminal A-subtype breast cancer who had undergone breast-conserving surgery. Patients received adjuvant endocrine therapy with no radiation therapy. Eligible tumors were estrogen receptor-positive (≥1%), progesterone receptor-positive (>20%), and HER2-negative, and had Ki-67 index ≤13.25%. Ductal, tubular, and mucinous histology was allowed, whereas lobular carcinoma was not.

Patients were followed clinically every 6 months for 2 years and annually thereafter. Annual mammograms were obtained, and patients were interviewed about adherence to adjuvant endocrine therapy. Patients' median age was 67 years; only 12% were aged 75 and older. The median tumor size was 1.1 cm. Adjuvant endocrine therapy was an aromatase inhibitor in 59% of patients and tamoxifen in 41%.

At 5 years, the rate of local recurrence in the ipsilateral breast was 2.3% (10 patients), which met the trial's prespecified boundary of ≤5%.