1. In a phase III trial of over 600 patients with good-risk ductal carcinoma in-situ (DCIS) of the breast, adjuvant radiation therapy (RT) was associated with decreased local recurrence compared to observation alone after surgery.
2. The overall survival between RT and observation arms was the same, with the RT group experiencing significantly more treatment-related toxicities.
Evidence Rating Level: 1 (Excellent)
Study Rundown: Ductal carcinoma in situ (DCIS) is the fourth most commonly diagnosed cancer in women in the United States. The National Surgical Adjuvant Breast and Bowel Project (NSABP) trial has previously demonstrated that combination breast conserving therapy (BCS) and adjuvant radiation therapy (RT) was equivalent to mastectomy, with significantly less morbidity. Recently, DCIS has recently been stratified into additional risk groups based on pathological features, with good-risk DCIS having relatively lower recurrence rates. The purpose of this trial was to compare RT after BCS and observation alone after BCS in patients with good-risk DCIS. This phase III trial enrolled over 600 patients with good-risk DCIS and assigned these patients to receive either RT or observation after BCS. After a median follow-up of 7 years, patients in the observation arm experienced significantly higher local recurrence compared to those in the RT arm. However, the absolute recurrence rate of the observation arm remained low (7.2%) and the overall survival was similar between the two arms. Furthermore, patients in the RT arm experienced significantly higher rates of low grade toxicities. The results of this trial support the conclusion that adjuvant RT reduces the rate of local recurrence compared to observation, but does not improve overall survival. Limitations of this study included the lack of proper stratification of hormone therapy use between the two groups and the relatively short follow-up time for detection of recurrence. Furthermore, breast irradiation practice has changed significantly during the trial period; future subset analysis of toxicity in hypofractionated therapy would be more relevant to current clinical practice.
Relevant Reading: Does Locoregional Radiation Therapy Improve Survival in Breast Cancer?
In-Depth [randomized controlled trial]: The Radiation Therapy Oncology Group (RTOG) 9804 study is a phase III randomized controlled trial analyzing the benefit of adjuvant radiotherapy (RT) after breast-conserving surgery (BCS) in low risk DCIS. Overall, 636 patients were recruited from 1998 to 2006 and randomized to either RT (n=312) or observation (n=317) after BCS. The median age of patients was 58 years, and study arms were balanced for Tamoxifen use and other clinical characteristics. The primary endpoint was ipsilateral local failure/recurrence. After a median follow-up time of 7.17 years, local failure among all patients enrolled in the observation only group was 7.2% compared with 0.8% in the RT group (HR: 0.10; 95% CI: 0.02-0.41; P<0.001). Disease free survival was not significantly different between the RT arm and observation arm (HR: 0.84; 95% CI: 0.53-1.32; P=0.44). Grade 1 and 2 acute toxicities was seen in 76% of the RT arm and 30% in the observation arm (P<0.001) while grade 3 or higher toxicities was seen in 4% of both arms (non-significant).
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