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Adjuvant radiotherapy (RT) for early breast cancer protected against ipsilateral recurrence for 10 years after treatment but not thereafter, according to long-term follow-up from a randomized trial.

After a median follow-up of 17.5 years, patients treated with adjuvant RT had a 61% lower risk of ipsilateral recurrence. However, the overall difference was driven by a 76% reduction in the hazard ratio (HR) during the first 10 years. Thereafter, the risk of ipsilateral recurrence was similar between patients who did and did not receive adjuvant RT. Overall survival (OS) also did not differ between the two groups, reported Linda J. Williams, PhD, of the University of Edinburgh in Scotland, and co-authors in .

"The results can help clinicians to advise patients better about their choice to have radiotherapy or not if they better understand what benefits it does or does not bring," the authors wrote of their findings. "These results might provide clues perhaps to the biology of radiotherapy benefit, given that it does not prevent late recurrence, suggesting that patients whose biology predicts a late relapse only might not gain a benefit from radiotherapy. This is a hypothesis to be tested."

The study adds to growing evidence that RT after breast-conserving surgery is not indicated for every patient but failed to provide new insight into a lingering question, according to the authors of an .

"The characteristics and identification of the individual patients that might benefit from [RT] omission remain unclear," noted Hans-Christian Kolberg, MD, of Marienhospital Bottrop in Germany, and Cornelia Kolberg-Liedtke, MD, PhD, of the University of Health Sciences in Bochum, Germany.

Previous studies have evaluated age cutoff, gene panels, and MRI results for identifying low-risk patients who might safely avoid RT. All provided promising information but had notable limitations.

"[The new] data add to the increasing perception that adjuvant radiotherapy might safely be de-escalated in select patient populations with early breast cancer," Kolberg and Kolberg-Liedtke wrote. "However, the identification of distinct patient subgroups who might not need adjuvant radiotherapy will remain a challenge for future scientific cohorts."

Williams and colleagues reported 30-year results from the Scottish Breast Conservation Trial, launched in 1985 to compare breast-conserving treatment with or without adjuvant RT. Previous similar studies accumulated 5- to 10-year follow-up, but few had issued reports with ≥20 years of follow-up.

Patients eligible for the trial were younger than 70, and had T1/2 N0/1 breast cancer treated with lumpectomy, lymph node sampling or clearance, and adjuvant systemic therapy. They were randomized to high-dose local or locoregional RT (50 Gy in 20-25 fractions) or no RT, and the primary endpoint was ipsilateral recurrence. The from the study, after 5.7 years of follow-up, showed an 80% reduction in the hazard with RT, but no OS benefit.

The trial originally included 585 patients, of whom 443 had died by the time of the current follow-up report. The updated analysis still showed no difference in median OS -- 19.2 years in the RT group and 18.7 years for the no-RT group. The 30-year OS rate was 23.7% with RT and 27.5% without.

The authors noted a "distinct difference" in ipsilateral recurrence over time. During the first decade after treatment, ipsilateral recurrence was significantly lower in the RT group (HR 0.24, 95% CI 0.15-0.38, P<0.001). Thereafter, the recurrence risk was almost identical (HR 0.98, 95% CI 0.54-1.79).

Summarizing the added value of the study, the authors reiterated that the overall reduction in ipsilateral recurrence with RT was driven by a large risk reduction during the first 10 years of follow-up. Median OS was similar, but the trial lacked statistical power to detect a small difference, if one existed.

"Reassuringly, omission of radiotherapy did not increase the distant metastasis rate," they noted.

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