Benefits of adjuvant radiotherapy for early breast cancer last a decade
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Key takeaways:
- Radiotherapy after breast-conserving surgery for early breast cancer protected against recurrence for 10 years.
- The protective effect diminished after a decade.
Adjuvant radiotherapy reduced risk for local recurrence for a decade among women with early breast cancer who underwent breast-conserving surgery, results of a randomized phase 3 trial showed.
However, benefits did not persist beyond 10 years, and OS did not differ between women who received radiotherapy and those who did not.
“[Women] whose tumors predict for late relapse beyond the first decade gain little from radiotherapy,” Ian H. Kunkler, MB, BChir, consultant clinical oncologist and professor of clinical oncology at The University of Edinburgh in Scotland, told Healio.
Background and methods
Prior research showed approximately 5% of women who undergo breast-conserving surgery and receive postoperative radiotherapy develop local recurrence in the first 10 years, according to study background.
However, data are limited regarding risk for recurrence beyond a decade after surgery.
Kunkler and colleagues published a 30-year update of the Scotting Breast Conservation Trial, which enrolled women aged younger than 70 years (median age, 57 years) with early-stage breast cancer (tumors 4 cm or less) between April 1, 1985, and Oct. 2, 1991.
The analysis included 585 women randomly assigned to postoperative radiotherapy (n = 291) or no radiotherapy (n = 294).
Median follow-up was 17.5 years.
Ipsilateral breast tumor recurrence and OS served as dual primary endpoints. Locoregional and regional recurrence, distant recurrence, EFS and breast cancer-specific survival served as secondary endpoints.
Results and next steps
Results showed significantly reduced risk for ipsilateral breast tumor recurrence in the radiotherapy group (HR = 0.39; 95% CI, 0.28-0.55).
However, the majority of the protective benefit against local recurrence occurred in the first decade after treatment (HR = 0.24; 95% CI, 0.15-0.38). After that time, risk for ipsilateral breast tumor recurrence appeared similar in the radiotherapy and no-radiotherapy groups (HR = 0.98; 95% CI, 0.54-1.79).
“We were surprised that the benefits of postoperative radiotherapy were time-dependent,” Kunkler said.
Results showed no significant difference in OS between the radiotherapy and no-radiotherapy groups (median, 19.2 years vs. 18.7 years; HR = 1.08; 95% CI, 0.89-1.3).
Researchers observed a higher rate of breast cancer mortality in the no-radiotherapy group (46% vs. 37%; P = .054). However, a higher percentage of women in the radiotherapy group than non-radiotherapy group died due to other cancers (20% vs. 11%; P = .012).
Kunkler and colleagues acknowledged study limitations, including the fact the trial began more than 40 years earlier, predating the development of better systemic therapies and improved imaging. In addition, researchers did not have data about acute or late radiation toxicity.
“Our findings should not discourage patients eligible for radiotherapy from receiving it, but [they should] encourage funders to support the long-term follow-up of breast cancer trials beyond the first decade to assess risks and benefits of treatment in the longer term,” Kunkler told Healio.
“We need further research to identify the biological mechanisms undertaking local breast recurrence beyond the first decade, such as tumor dormancy and reactivation,” he added. “We will need to see the results of long-term follow-up of other trials of postoperative radiotherapy similar in design to our own to see if the findings of a lack of ‘carry over’ effect of radiotherapy is replicated at the same, earlier or later point.”
For more information:
Ian Kunkler, MB, BChir, can be reached at i.kunkler@ed.ac.uk.
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