WEDNESDAY, Aug. 21, 2024 (HealthDay News) — In women with early breast cancer, radiation therapy could prevent the recurrence of ipsilateral breast cancer for 10 years but offers no benefit after that, according to a study published online Aug. 7 in The Lancet Oncology.

Linda J. Williams, Ph.D., of the University of Edinburgh in the United Kingdom, and colleagues conducted a randomized, controlled phase 3 trial in 14 hospitals in Scotland involving women under 70 years of age with early breast cancer. Patients underwent breast-conserving surgery and received tamoxifen (estrogen receptor (ER)-rich patients) or chemotherapy (ER-poor patients) for five years and were then randomly assigned to receive high-dose local or locoregional radiotherapy or no radiotherapy (291 and 294, respectively, after excluding four ineligible patients).

Patients were followed for a median of 17.5 years. The researchers found that ipsilateral breast tumor recurrence was significantly lower in the radiotherapy group than in the no radiotherapy group (16 versus 36 percent; hazard ratio, 0.39). There were differences in the risk of ipsilateral breast tumor recurrence in the first decade after treatment (hazard ratio, 0.24), but both groups had similar subsequent risks of ipsilateral breast tumor recurrence. There was no difference in overall survival between the groups (median 18.7 versus 19.2 years in the no radiotherapy group and the radiotherapy group, respectively).

“This study may provide clues to the biology underlying the benefit of radiotherapy over time, as it does not appear to prevent late local recurrence,” the authors write. “This suggests that patients whose biology predicts late relapse benefit little from radiotherapy, a hypothesis that remains to be tested.”

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