BENEFITS OF RADIATION THERAPY IN EARLY BREAST CANCER

November 3, 2010 (San Diego, California) — Further evidence that radiation therapy after breast-conserving surgery reduces the risk for recurrence or death from breast cancer comes from a new meta-analysis, presented here at the American Society for Radiation Oncology 52nd Annual Meeting. The new data also show a reduction in all-cause mortality.

The results of the analysis of a combined cohort of almost 11,000 women show that adding radiation to breast-conserving therapy lowers the risk for recurrence within 10 years by nearly 15%.

"The effect of radiotherapy on breast cancer mortality is very little in the first 5 years after randomization, but by 15 years, there is a very clear effect on breast cancer mortality, with a 3.8% reduction," said study author Sarah Darby, PhD, professor of medical statistics at the Clinical Trial Service Unit and Epidemiological Studies Unit at Oxford University, United Kingdom.

"Most important," she added, "radiotherapy not only reduces breast cancer mortality, but also all-cause mortality — by 3% at 15 years after randomization."

Although this confirms what we already know about radiation therapy in early breast cancer, this study provides further evidence of a larger magnitude, she told Medscape Medical News.

"This study also shows that there is a real survival benefit, not just a benefit for local recurrence," said Dr. Wilson, professor of therapeutic radiology and dermatology at Yale University School of Medicine, New Haven, Connecticut, who was not involved with the study. "It definitely adds to the evidence."

Impact Greater in Certain Subgroups

Although there is much evidence to support the use of radiation therapy after breast-conserving therapy, it might be more effective for certain types of breast cancer than for other types. To examine the evidence of any such differences, and to quantify them when appropriate, collaborative meta-analyses were undertaken.

Dr. Darby and colleagues reviewed data from studies that had begun by 2000 (and were initiated between 1976 and 1999). A total of 10,906 women from 17 randomized trials were included in the analysis, which had a median follow-up period of 9.5 years.

In addition to reducing overall risk for recurrence, the authors found that the impact of radiation varied among the different subtypes of breast cancer. Most notably, radiation therapy conferred a substantial benefit on women with node-positive disease and on women with higher-risk node-negative disease in terms of the 10-year risk for any recurrence of breast cancer and the 15-year risk for breast-cancer-related mortality.

For the 7334 patients with pathologically node-negative breast cancer, radiation therapy decreased the 10-year risk for isolated loco-regional recurrence by 15.4% (7.1% vs 22.5%) and the 10-year risk for any recurrence by 14.5% (18.9% vs 33.4%).

Among this subgroup, the reduction in risk varied according to confounders, such as age, grade, estrogen-receptor (ER) status in combination with tamoxifen use, and extent of surgery.

As an example, note the authors, women with ER-positive tumors participating in trials where breast-conserving surgery was performed and tamoxifen was planned, the 10-year reduction in the risk for recurrence in women younger than 40 years with high-grade tumors was 35%. In contrast, for women 70 years and older with low-grade tumors, it was only 5%.

Among the 1108 women with pathologically node-positive disease, radiation therapy reduced the 10-year risk for isolated loco-regional recurrence by 30.8% (42.7% vs 11.9%), but the impact was lower for the risk for any recurrence (17.7%; 46.8% vs 64.5%; P < .00001). This difference is due to the higher percentage of women in this group with distant recurrence or a contralateral breast cancer as their first event by the 10th year, the authors explain.

Also, within this subgroup, radiotherapy reduced the 15-year risk for breast-cancer-related mortality by 7.8% (43.4% vs 51.2%; P = .04).

American Society for Radiation Oncology (ASTRO) 52nd Annual Meeting: Abstract LB2. Presented November 1, 2010.