NSABP B-17
After complete excision of localized DCIS with negative margins, does whole-breast radiotherapy reduce ipsilateral breast recurrence compared with lumpectomy alone?
Absolute Effect
Overall survival was not materially different because deaths from breast cancer were uncommon; the principal benefit was local/ipsilateral control.
At 5 years, event-free survival was 84.4% with RT vs 73.8% without RT (absolute +10.6 points; P=.001).
Treatment burden and toxicity
The major treatment burden was addition of whole-breast RT. No major excess in regional/distant events or breast-cancer mortality was demonstrated. Radiation reduced both invasive and non-invasive ipsilateral tumours.
Quality of life: No modern patient-reported QoL endpoint was central to the original trial.
Subgroups / clinically important modifiers
All examined clinical/mammographic subgroups benefited from RT in the 8-year report.
Limitations and maturity
Older RT technique and DCIS diagnostic era; systemic/endocrine selection was not the modern ER-directed pathway. The endpoint was recurrence, not overall survival.
Clinical interpretation
This is the foundational randomized evidence for adding RT after breast-conserving surgery for DCIS and provides the comparator against which later RT-omission studies should be interpreted.