👉The Radiation Therapy Oncology Group (RTOG) 9804 trial evaluated the impact of RT after breast-conserving therapy (BCT) in patients with mammographically detected low-risk DCIS as defined by size <2.5 cm, unicentricity, low- and intermediate-grade, and margins >3 mm.
👉Data were analyzed after a median follow-up of 7.17 years in 636 patients randomly assigned to either RT or observation after BCT.
👉The primary endpoint of ipsilateral local failure was 0.9% in the RT arm versus 6.7% in the observation arm.
PATIENTS AND METHODS:
👉This prospective randomized trial (1998 to 2006) in women with mammographically detected low- or intermediate-grade DCIS, measuring less than 2.5 cm with margins ≥ 3 mm, compared RT with observation after surgery.
👉The study was designed for 1,790 patients but was closed early because of lower than projected accrual.
👉Six hundred thirty-six patients from the United States and Canada were entered; tamoxifen use (62%) was optional.
👉Ipsilateral local failure (LF) was the primary end point; LF and contralateral failure were estimated using cumulative incidence, and overall and disease-free survival were estimated using the Kaplan-Meier method.
👉Median follow-up time was 7.17 years (range, 0.01 to 11.33 years).
👉Two LFs occurred in the RT arm, and 19 occurred in the observation arm.
👉At 7 years, the LF rate was 0.9% (95% CI, 0.0% to 2.2%) in the RT arm versus 6.7% (95% CI, 3.2% to 9.6%) in the observation arm (hazard ratio, 0.11; 95% CI, 0.03 to 0.47; P < .001).
👉Grade 1 to 2 acute toxicities occurred in 30% and 76% of patients in the observation and RT arms, respectively; grade 3 or 4 toxicities occurred in 4.0% and 4.2% of patients, respectively.
👉Late RT toxicity was grade 1 in 30%, grade 2 in 4.6%, and grade 3 in 0.7% of patients.
👉In this good-risk subset of patients with DCIS, with a median follow-up of 7 years, the LF rate was low with observation but was decreased significantly with the addition of RT. Longer follow-up is planned because the timeline for LF in this setting seems protracted.
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