A new meta-analysis of previous studies has reported that radiation treatment after breast-conserving surgery (typically, lumpectomy) substantially reduces long-term breast cancer recurrence and breast cancer-specific death. Radiation treatment after breast-conserving surgery is known to reduce breast cancer recurrence and breast cancer-specific death.
However, radiation may have more benefits for some types of patients than others. To conduct the study, the authors performed a meta-analysis of individual patient data for 10,801 women in 17 randomized European and North American trials of radiation treatment compared to no radiation after breast-conserving surgery. Pathologically confirmed lymph node status was available for 8,337 of the women.
Radiation treatment was found to reduce the 10-year risk of recurrence from 35.0% to 19.3% and the 15-year risk of breast cancer-specific death from 25.2% to 21.4% in the study group overall. In the 7,287 women with lymph node negative disease, radiotherapy reduced the 10-year risk of recurrence from 31.0% to 15.6% and the 15-year risk of breast cancer-specific death from 20.5% to 17.2%. The absolute recurrence reduction in lymph node negative women was found to vary according to age, tumor grade, estrogen receptor status, tamoxifen use, and extent of surgery. In the 1,050 women with lymph node positive disease, radiation was found to reduce the 10-year recurrence risk from 63.7% to 42.5% and the 15-year risk of breast cancer-specific death from 51.3% to 42.8%. Overall, approximately one breast cancer death was averted by year 15 for every four recurrences avoided by year 10. The authors conclude that radiotherapy after breast-conserving surgery halves the rate of disease recurrence and reduces breast cancer mortality rate by about a sixth. These proportional benefits vary little between different groups of women. On the other hand, the absolute benefits from radiotherapy vary substantially according to the characteristics of the patient and they can be predicted at the time when treatment decisions need to be made.

Comments regarding the study

In a separate interview, study author Sarah C. Darby noted that the analysis means that radiation prevents recurrences for a longer time and saves more lives than was previously recognized. The positive impact of radiation treatment has been underestimated because it takes five years to show up. “These data reinforce the fact that the recurrence rate is reduced for the whole of the first decade,” Darby said. In addition, the study helps to counter two theories that have been used to de-emphasize the importance of radiation after breast conserving surgery.
The first is that since radiation is a local treatment which prevents locoregional recurrence, any such recurrence will likely be caught and treated. As Darby points out, the study results show that “if somebody has a local recurrence, yes, you can treat it, but before that happens, some of that residual cancer will have spread.” The second hypothesis countered by the study results is the idea that if a cancer has the tendency to spread, it will do so even before the tumor surgery, so that radiation treatment would be too late to stop it. Instead, the results show that radiation appears to help prevent late recurrences.