(MedPage Today) -- Radiation therapy following breast conserving surgery reduced the rate of disease recurrence by half, a large meta-analysis found.
In trials of more than 10,000 women with breast cancer, the use of radiation therapy decreased the risk of recurrence within 10 years from 35% to 19.3%, according to investigators from the Early Breast Cancer Trialists' Collaborative Group (EBCTCG).
That represented an absolute reduction of 15.7% (95% CI 13.7 to 17.7, 2P<0.00001), the investigators reported online in The Lancet.
Because the possibility that microscopic remnants of tumor may remain with breast conserving surgery, radiation has often been used with the aim of preventing recurrences and metastases.
However, the long-term outcomes of these efforts have not been fully chronicled, so the EBCTCG have been following their large cohort of clinical trial participants and periodically updating their outcomes data.
The current report included 17 trials that began before 2000, six of which evaluated the use of radiation therapy after lumpectomy in 4,398 low- and high-risk women.
Four of the trials examined the results of radiotherapy after quadrantectomy or sector resection in 2,399 women. The remaining seven compared radiotherapy following lumpectomy in 4,004 women considered to be at low risk.
This analysis found that not only did radiotherapy reduce the rate of 10-year recurrences, but also decreased the 15-year mortality risk by 3.8% (95% CI 1.6 to 6, 2P=0.00005), the investigators reported.
Women who had radiation therapy after their surgery also had half the annual rate of a first recurrence compared with those not given radiotherapy (RR 0.52, 95% CI 0.48 to 0.56), with the greatest benefit seen during year one (RR 0.31, 95% CI 0.26 to 0.37).
The annual death rate was reduced with the use of radiation therapy by about one-sixth (RR 0.82, 95% CI 0.75 to 0.90).
The investigators also looked at differences depending on whether the women had lymph node positive or negative disease.
Among those who were lymph node negative and had radiotherapy, the annual recurrence rate during the first 10 years fell by about half (RR 0.46, 95% CI 0.41 to 0.51).
This decreased the 10-year recurrence risk to 15.6% from 31%, which represented an absolute risk reduction of 15.4% (95% CI 13.2 to 17.6, 2P<0.00001), the investigators found.
These lymph node negative women also had a decrease in mortality over 15 years, to 17.2% from 20.5%, which was an absolute risk reduction of 3.3% (95% CI 0.8 to 5.8, 2P=0.005).
Women who were lymph node positive and received radiation therapy experienced a five-fold decrease in recurrences during the first year, from 26% to 5.1% (RR 0.20, 95% CI 0.14 to 0.29), according to the investigators.
Mortality also was reduced in lymph node positive women who had radiotherapy (RR 0.79, 95% CI 0.65 to 0.95, 2P=0.01).
Further analyses of patient subgroups determined that absolute reduction in recurrences was significantly associated with age (2P=0.0002), tumor grade (2P<0.00001), and estrogen receptor status and use of tamoxifen (2P=0.003).
Finally, the investigators calculated that among the entire cohort, by year 15 one death was prevented for every four recurrences prevented at year 10.
They noted that the risk reduction was less in the most recent trials with the wider use of tamoxifen.
"However, even for women with [lymph node negative] disease in the recent low-risk trials, the predicted absolute 10-year recurrence reduction with radiotherapy exceeded 10% in most women and exceeded 20% in some women," they observed.
In a comment accompanying the meta-analysis, Thomas A. Buchholz, MD, of the University of Texas MD Anderson Cancer Center in Houston, observed, "These results confirm that radiation is effective in eradication of much of the microscopic locoregional disease that might still be present after surgery."
"The data reinforce the important role that radiotherapy has in management of breast cancer, and the fact that the benefits of radiation are complementary to the advances in both surgery and systemic treatment is particularly rewarding," Buchholz wrote.
The Early Breast Cancer Trialists' Collaborative Group is funded by Cancer Research UK, the British Heart Foundation, and the UK Medical Research Council.
The secretariat and writing committee members of the collaborative group declared that they had no conflicts of interest.
Primary source: The Lancet Source reference: Darby S, et al "Effect of radiotherapy after breast-conserving surgery on 10-year recurrence and 15-year breast cancer death: Meta-analysis of individual patient data for 10,801 women in 17 randomized trials" Lancet 2011; DOI: 10.1016/S0140-6736(11)61629-2.Additional source: The LancetSource reference: Buchholz T "Radiotherapy and survival in breast cancer" Lancet 2011; DOI: 10.1016/S0140-6736(11)61296-8