PHILADELPHIAAfter 8 years' follow-up, tamoxifen plus breast radiation resulted in a lower rate of ipsilateral breast relapse than tamoxifen alone in women over 50 with early-stage, node-negative breast cancer treated initially with lumpectomy. Anthony W. Fyles, MD, of Princess Margaret Hospital and the University of Toronto, reported the results at the American Society for Therapeutic Radiology and Oncology (ASTRO) 48th Annual Meeting (abstract 8).
This analysis, an update of previous results from a randomized trial conducted at two Canadian centers, reflects investigators' continuing search for a category of women at sufficiently low risk for breast cancer recurrence that they might avoid radiation therapy.
Dr. Fyles compared his results to those of four other clinical trials of radiation added to tamoxifen that have failed to clearly define such a low-risk group. An unplanned subgroup analysis of the Canadian trial suggests "if one were to select patients who might be treated with hormones alone, we should include only those with tumors 1 cm or less and age 60 or above," he said. Even to make a recommendation in that group, "confirmatory results would be necessary."
The Canadian study, conducted at Princess Margaret Hospital and the British Columbia Cancer Agency, Vancouver, included 769 women with stage 0 or I, node-negative breast cancer. After lumpectomy and axillary dissection, all patients received standard-dose tamoxifen (20 mg/d for 5 years), and half, by random assignment, underwent breast radiation. According to the previously reported 5-year results, local recurrence was documented in 0.6% of women who received radiation/tamoxifen vs 7.7% of women who received tamoxifen alone (P < .001).
These initial results paralleled several other clinical trials of similar design, but with different entry criteria. Overall relapse rates showed striking differences among the studies, suggesting it might be possible to identify a group of low-risk patients who could forgo breast irradiation. The updated analysis was conducted in part to identify such a risk group, which was prospectively defined as patients with "a breast relapse rate of 5% or less at 8 years. Many of these relapses would be salvageable, and they would have little impact on overall survival," Dr. Fyles said.
In the Canadian study, overall outcomes at 8 years still favored radiation therapy, with a 12.2% incidence of ipsilateral breast relapse in the tamoxifen-only arm and a 4.1% rate in the radiotherapy plus tamoxifen group (P < .0001).
Results in subgroups from this study were analyzed and compared with previously published results from the CALGB (Cancer and Leukemia Group B) trial C9343 (N Engl J Med 351:971-977, 2004). Women in the CALGB study were age 70 or older and had tumors 2 cm or less in size that were node-negative and estrogen-receptor (ER) positive. These patients experienced a 1% 8-year relapse rate with tamoxifen plus radiation and a 4% rate with tamoxifen alone (P < .001).