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Breast: DCIS management and radiotherapy

Free question published 04 October 2026

BreastDCIS management and radiotherapy

A 59-year-old postmenopausal woman has undergone breast-conserving surgery for a 15 mm area of intermediate-grade ductal carcinoma in situ (DCIS), excised with clear margins. There is no invasive component. She is anxious to avoid recurrence and asks what adjuvant radiotherapy would offer. What is the most accurate statement about whole-breast radiotherapy after breast-conserving surgery for DCIS?

  1. AIt reduces only in-situ recurrence, not invasive recurrence
  2. BIt reduces ipsilateral breast recurrence significantly and improves overall survival outcomes substantially
  3. CIt has no effect on ipsilateral breast events in DCIS
  4. DIt approximately halves the risk of ipsilateral breast event but does not improve mortality
  5. EIt is only of benefit when margins are involved

Why D is correct

The EBCTCG overview of the four randomised DCIS trials showed radiotherapy after breast-conserving surgery reduced the absolute 10-year risk of any ipsilateral breast event (recurrent DCIS or invasive cancer) by 15.2% (28.1% without radiotherapy versus 12.9% with), roughly halving the recurrence rate, with similar reductions for in-situ and invasive recurrences, but with no significant effect on breast cancer mortality. NICE NG101 accordingly recommends considering adjuvant radiotherapy after breast-conserving surgery for DCIS with clear margins.

And why the others are not

  • AIncorrect. Radiotherapy reduced both in-situ and invasive ipsilateral recurrences, not in-situ alone.
  • BIncorrect. The overview showed no significant effect on breast cancer mortality, so a survival benefit cannot be claimed.
  • CIncorrect. Radiotherapy clearly reduced ipsilateral breast events.
  • EIncorrect. The recurrence reduction applies after breast-conserving surgery with clear margins, not only when margins are involved.

Source EBCTCG overview - radiotherapy in ductal carcinoma in situ (DCIS) — Early Breast Cancer Trialists' Collaborative Group (EBCTCG), Correa C, McGale P, Taylor C, et al. Overview of the randomized trials of radiotherapy in ductal carcinoma in situ of the breast. J Natl Cancer Inst Monogr. 2010;2010(41):162-177.

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