Efficacy
The Ductal Carcinoma In Situ (DCIS) Cochrane review by Goodwin et al. included 4 randomised control trials: NSABP B-17, EORTC10853, UKCCCR and SweDCIS.26 The review compared the addition of radiation therapy to breast conserving surgery (BCS) (n = 3925 women). They reported a statistically significant benefit from the addition of radiation therapy on all ipsilateral breast events (Hazard Ratio (HR) 0.49, 95% CI: 0.41-0.59, p <0.00001) and ipsilateral recurrence (HR 0.64, 95% CI: 0.41 to 1.01, p = 0.05).26 The addition of radiation therapy reduced the risk of recurrence of either DCIS or invasive cancer in the treated breast by 51%.
The 15-year combined analysis of the NSABP B-17 and B-24 trials showed the reduction in risk of local recurrence appeared to persist in the long term.28 The ipsilateral breast recurrence rate was reduced from 19.4% to 8.9% with radiation therapy at 15 years. The overall survival (OS) rate was similar, 83% versus 84%.
Further evidence supporting this protocol was provided by a second meta-analysis by Correa et al.27 This meta-analysis reviewed individual patient data for the same 4 trials (n = 3925 women) and also compared BCS alone to BCS with adjuvant radiation therapy. The 10-year ipsilateral breast recurrence rate with surgery alone was statistically significant, 28% compared to 13% for BCS with radiation therapy. This benefit was greater in women >50 years old (28% versus 11%) compared with women <50 years old (29% versus 18%). Women with small, low-grade tumours and negative surgical margins still benefited (30% versus 12%, statistically significant). There was no effect on breast cancer specific mortality (~4%), other-cause mortality (~5%), and all-cause mortality (~8%).
A meta-analysis conducted by Stuart et al. included 9391 patients with follow-up at 10 years reported adjuvant radiation therapy after BCS was associated with greater local control when compared to patients who were managed with BCS and biopsy alone.29 At 10 years, OS was similar in patients treated with mastectomy or breast conserving surgery with or without radiation therapy.
Bijker et al. reported the inclusion of radiation therapy resulted in a 48% reduction in the 10-year local recurrence (LR) rate in DCIS (14% with BSC versus 7% with BSC and radiation therapy, statistically significant). Factors that increased the risk for LR were age <40 years old, grade 2 or 3, cribriform or solid growth pattern, doubtful margin, and local excision alone. Size was not a prognostic factor. There was no difference reported in OS or distant metastases.31
In 20-year follow-up the sweDCIS trial showed the absolute risk reduction of ipsilateral breast recurrence in the radiation therapy arm was 12.0% at 20 years (95% CI: 6.5-17.7), with a relative risk reduction of 37.5%.33 Absolute reduction was 10.0% (95% CI: 6.0-14.0) for DCIS. The cumulative incidence of invasive ipsilateral recurrences was found to continuously rise over the 20-year period before plateauing.
Role of hypofractionation and boost
TROG 07.01 was a phase III randomised control trial assessing the addition of sequential tumour bed boost following conventional or moderately hypofractionated whole breast irradiation in patients with non-low-risk DCIS.13 Non-low-risk DCIS included patients aged <50 years old, symptomatic presentation, palpable tumour, microscopic tumour size measuring ≥15 mm, multifocal disease, intermediate or high nuclear grade, central necrosis, comedo-histology, or a radial surgical margin of <10 mm, or a combination. The 5-year free from local recurrence rates were 93% in the no boost group and 97% in the boost group (HR 0.47, 95% CI: 0.31-0.72, p <0.001). There was no statistically significant difference in 5-year overall survival rates between the no-boost (98.2%) and boost (99.0%) groups. When comparing conventional fractionation to moderate hypofractionation, there were no significant differences observed in the 5-year free from local recurrence rates. Boost, but not hypofractionation, is associated with higher incidence of grade 2 or greater breast pain (10% in no-boost vs 14% in boost, p=0.003) and induration (6% vs 14%, p<0.001).
Simultaneous integrated boost (SIB) is safe and reduces patient visits for invasive breast cancer, and data could be extrapolated for DCIS. IMPORT-HIGH randomised 2621 women who completed breast conserving surgery for T1-3, pN0-3a, M0 tumours in a 1:1:1 fashion.34 The control group received 40 Gy in 15 fractions to the whole breast followed by 16 Gy in 8 fractions sequential photon boost to the tumour bed volume, test group 1 received 36 Gy in 15 fractions to the whole breast, 40 Gy in 15 fractions to partial breast and 48 Gy in 15 fractions concomitant photon boost to the tumour bed volume, and test group 2 received 36 Gy in 15 fractions to the whole breast, 40 Gy in 15 fractions to partial breast and 53 Gy in 15 fractions concomitant photon boost to the tumour bed volume. 48 Gy SIB (test group 1) delivered in 3 weeks had similar efficacy to sequential boost delivered over 4-5 weeks, with similar or milder rates of adverse events. 53 Gy SIB (test group 2) had no additional benefit in local cancer control but a higher risk of moderate or marked breast induration.
Optimal margins
Although it is widely accepted that positive margins definitively increase the risk of locoregional recurrence (LRR) in patients who undergo BCS even with adjuvant radiation therapy, the exact optimal margin threshold is not yet defined at an international level.30, 39, 40
ASTRO guidelines and other eminent groups recommend a >2 mm margin.3, 4, 30, 10, 5 Other groups infer smaller margins may be acceptable in selected cases.5, 41, 42
Tadros et al. recently published a retrospective analysis of a cohort of 1491 ‘contemporary’ patients with DCIS.36 They reported no statistically significant difference in locoregional control between patients with <2 mm and ≥2 mm negative margins who underwent adjuvant radiation therapy. For patients who did not undergo adjuvant radiation therapy however, those with margins <2 mm were significantly more likely to develop LRR than those with margins ≥2 mm.
Van Zee et al. echoed the above in their retrospective analysis of 2996 patients.37 They reported no significant association between negative margin width and risk of LRR for patients who received adjuvant radiation therapy, however, in patients with smaller negative margins who did not receive radiation therapy there was a significant risk of LRR.
The 2016 ASTRO guidelines noted that clinical judgement must be used when deciding on the need for re-excision in patients with >0-1 mm margins. Factors to consider include residual calcifications on post-excision mammography, extent of DCIS in proximity to margin, which margin is close (superficial/deep versus radial), cosmetic impact of re-excision, and overall life expectancy.5
The reference committee consensus is that clear margins ≥2 mm is optimal, however; narrower margins may be acceptable in selected cases.
Low-risk subgroups
Omission of radiation therapy may be considered in some low-risk patients such as those who were eligible for RTOG 9804 Good-Risk DCIS trial.43 However, with longer follow-up (median 13.9 years), a steady increase of 1% per year of ipsilateral breast recurrence (IBR) was observed up to at least 15 years.6In this population, the use of radiation therapy reduced IBR with a HR of 0.36.
The RTOG 9804 eligibility criteria included:
- mammogram detected DCIS or incidental finding of DCIS in tissue of an otherwise benign biopsy
- unicentric disease
- low or intermediate nuclear grade
- size <2.5 cm
- margin ≥3 mm to ink
- negative post-excision mammogram.
Although the benefit of the addition of radiation therapy has been demonstrated in all sub-groups of patients, absolute benefit in these patients is small (1% risk of recurrence per year is halved by the addition of radiation therapy).43The known and increasing long-term risk of a local recurrence must be considered in the context of a patient's longevity and wellbeing.
Consider the use of a DCIS recurrence risk tool to assist in decision making.
Chemoprevention
COSA provides a clinician guide for medications to lower the risk of breast cancer opens in a new tab or window.