After breast-conserving surgery, radiation therapy cut the rate of breast cancer recurrence in half and reduced the breast cancer death rate by one-sixth, according to a meta-analysis published online Oct. 20 in The Lancet.
The Early Breast Cancer Trialists’ Collaborative Group (EBCTCG) sought to determine the impact and magnitude of radiation therapy on breast cancer recurrence and death. It updated previous analyses with a meta-analysis of 10,801 women in 17 randomized trials and examined the data by patient and disease characteristics, specifically pathologically confirmed node-negative or node-positive disease.
The researchers calculated a 10-year risk of first recurrence of 19.3 percent in women allocated to radiation therapy and 35 percent in women allocated to surgery only. Radiation therapy also yielded a 3.8 percent reduction in absolute risk for breast cancer death over 15 years, which suggests one breast cancer death is avoided for every four recurrences avoided by radiation therapy.
For the 7,287 women with node-negative disease, radiation therapy halved the recurrence rate over 10 years and provided an absolute reduction of 15.4 percent. Among the 1,050 women with node-positive disease, radiation therapy provided a higher absolute reduction in recurrence over 10 years, at 21.2 percent.
EBCTCG researchers analyzed data by various subgroups and found that radiation therapy roughly halved annual recurrence rates among most subgroups. The absolute recurrence reduction in node-negative patients hinged on various factors: patient age, tumor grade, tumor size, estrogen receptor status and tamoxifen use, additional therapy and lumpectomy. Earlier trials indicated that young age, large tumor size and high grade each strongly predicted risk of locoregional recurrence and absolute reduction in risk.
“The overall findings from these trials show that radiotherapy after breast-conserving surgery not only substantially reduces the risk of recurrence but also moderately reduces the risk of death from breast cancer,” according to the researchers.
They divided women into four categories -- node-negative women with lower, intermediate and large predicted absolute recurrence benefit and node-positive women -- and found that the 15-year reduction in risk of breast cancer death in women with a large predicted benefit nearly reached that of those with node-positive disease. However, they noted that this classification had not been externally validated and should be interpreted with caution.
The researchers concluded by predicting that radiation therapy may continue to confer a benefit in conjunction with recent advances in treatment. "Screening, surgery, pathology, radiotherapy and systemic therapy have all changed substantially since most of these women were randomly assigned, so the absolute recurrence reduction with radiotherapy in future patients might differ greatly from that recorded in these trials. Moreover, information about additional risk factors will often be available (e.g. HER2, gene expression profile, margin status) and a radiotherapy boost may be given. Nevertheless, the finding that radiotherapy roughly halved the recurrence rate after breast-conserving surgery in a wide range of patients with very different absolute risks suggests that it might also roughly halve the recurrence rate in future patients given breast-conserving surgery."
In an accompanying editorial, Thomas A. Buchholz, MD, from MD Anderson Cancer Center in Houston, noted that “the benefits of radiation are complementary to the advances in both surgery and systemic treatment…The incremental benefits of each component of treatment contributed to the ongoing success in reduction of breast cancer mortality rates.”