Background
Phase III, randomized non-inferiority trial. 636 patients with good-risk DCIS after BCS with clear margins (≥3mm): grade 1–2, size ≤2.5cm, mammographically detected. Tamoxifen was optional in both arms. Randomized to whole-breast RT (50Gy/25f) vs observation alone. Question: can RT be safely omitted in low-risk DCIS?
Interventions and follow up
Arm A: Whole-breast RT 50Gy in 25 fractions (tamoxifen optional)
Arm B: Observation, no RT (tamoxifen optional)
Primary endpoint: Ipsilateral breast tumor recurrence (IBTR)
mFollow up: 7.2 years
Arm B: Observation, no RT (tamoxifen optional)
Primary endpoint: Ipsilateral breast tumor recurrence (IBTR)
mFollow up: 7.2 years
Results
IBTR (7-yr): 0.9% (RT) vs 6.7% (observation), P<.001
Invasive IBTR (7-yr): 0.4% vs 3.5%
OS: Similar between arms (95.8% vs 95.6%)
Invasive IBTR (7-yr): 0.4% vs 3.5%
OS: Similar between arms (95.8% vs 95.6%)
Adverse events
Acute (RT arm): Grade 2 skin reactions during RT (transient).
Late (RT arm): Grade 1–2 breast fibrosis and cosmetic changes; grade ≥3 events uncommon.
Other: No significant difference in survival-limiting toxicities between arms.
Late (RT arm): Grade 1–2 breast fibrosis and cosmetic changes; grade ≥3 events uncommon.
Other: No significant difference in survival-limiting toxicities between arms.
Conclusions
Whole-breast RT significantly reduced IBTR in good-risk DCIS (by ~5.8% at 7 years) vs observation. Even in this favorable low-risk subgroup, RT substantially reduced local recurrence. The trial does not identify a population in which RT can be safely omitted in DCIS, though absolute event rates were low.
Key Limitations
Despite statistical significance, the 7-year absolute risk difference is 5.8% — whether this justifies RT in every good-risk patient requires individualized discussion. Very low IBTR rates in both arms make the OS comparison underpowered. Tamoxifen use was non-randomized. The low-risk DCIS criteria (grade 1–2, ≤2.5cm) may be further stratified in the modern era using genomic assays (Oncotype DX DCIS, DCISionRT). Ongoing trials (LORD, LORIS, COMET) prospectively test RT omission in selected DCIS.
Clinical Context
RTOG 9804 remains a definitive RCT showing RT reduces recurrence even in low-risk DCIS. Standard of care for DCIS after BCS remains RT ± endocrine therapy. Genomic profiling tools (DCISionRT, Oncotype DCIS Score) are increasingly integrated into practice to identify patients who may safely omit RT — pending mature data from LORD, LORIS, and COMET. ESMO-MCBS: not applicable (local recurrence endpoint, not survival).
References