Eligible tumors were 2.5 centimeters (cm) or smaller, with margins of three millimeters or less, and of low or intermediate nuclear grade. From 1999 to 2006, 636 patients were randomly assigned to receive WBRT with standard doses or to an observation arm. The use of tamoxifen for five years was optional. Initial results, including seven years of follow-up, were reported in 2013 and published in the Journal of Clinical Oncology in 2015.
The new analyses include long-term follow-up data for 629 patients whose median age was 58 years, including 76 percent post-menopausal women. Mean pathological tumor size was 0.60 centimeters (61 percent 0.5 cm or smaller, 65 percent with a margin width of 1.0 cm or larger or a completely negative re-excision specimen). The highest nuclear tumor grade was 1, found in 44 percent of patients; grade-2 tumors were diagnosed in the remaining 56 percent. Tamoxifen was used by 58 percent of patients on the WBRT arm and 65 percent of those on the observation arm (p=0.05).
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Median follow-up time was 12.4 years. After 12 years, the cumulative incidence of local recurrence was 2.8 percent (95% CI 1.1, 5.6) for those in the WBRT arm and 11.4 percent (7.7, 15.8) for those in the observation arm (hazard ratio (HR) 0.26, 95% CI 0.13, 0.54; p=0.0001). The 12-year cumulative incidence of invasive local recurrence was 1.5 percent (95% CI 0.4, 4.0) for those in the WBRT arm and 5.8 percent (3.2, 9.5) for those who did not receive radiation (HR 0.34, 95% CI 0.14, 0.85; p=0.016).
In multivariate analysis, only those who received both WBRT (HR 0.25, 95% CI 0.12, 0.53; p=0.0003) and tamoxifen (HR 0.50, 95% CI 0.27, 0.91; p=0.024) experienced reduced local recurrence. Neither age nor pathological tumor size were significant for predicting local recurrence or invasive local recurrence. There were no significant differences between treatment arms for overall survival, disease-free survival or mastectomy use.
During the additional five years following surgery, noted Dr. McCormick, "there was a slight creeping up of local recurrence rate." For those who received WBRT, the rate increased by just under 1 percent, bringing it to nearly 3 percent post-surgery. For those who did not receive radiation, the recurrence rate increased by one percentage point each additional year of follow-up, climbing from just under 7 percent to just under 12 percent after 12 years.
These results "should inform a meaningful patient-physician discussion that includes risks, benefits and the patient's own degree of comfort," Dr. McCormick concluded.
"All of us have a different definition of what is an acceptable risk," she said. "Some patients with DCIS will still want radiation therapy. But for others, the risk is so low they may opt not to treat, and that should be considered a viable option."
