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A large national study has provided some of the strongest evidence yet on how much healthy tissue should be removed when treating ductal carcinoma in situ (DCIS) with breast-conserving surgery – helping to resolve a long-running clinical debate and prompting changes to the Association of Breast Surgeons guidance.
Collaborating with Professor John Robertson at The University of Nottingham, who led the project, along with other institutes, researchers at The Institute of Cancer Research, London, in the Clinical Trials and Statistics Unit (ICR-CTSU) analysed data from breast cancer patients treated through the NHS Breast Screening Program to find that those with surgical margins – the edges of healthy tissue removed along with the tumour – of less than 2 mm faced an increased risk of the cancer returning than those whose margins were at least 2 mm wide. However, the study showed no added benefit from removing tissue beyond this threshold.
The findings, published in eClinicalMedicine, are based on one of the largest and longest-running real world analyses of DCIS surgical outcomes to date, with follow-up extending to 14 years in some patients.
Funding for the study came from a small grant from the Association of Breast Surgeons (ABS) to cover NHS England data access costs with The University of Notting sponsoring the project. The ICR-CTSU core receives funding through the Cancer Research UK core programme grant
A question without clear evidence
DCIS is a non-invasive form of breast cancer that is frequently detected through mammographic screening. Rather than undergoing a mastectomy, many women are treated with breast-conserving surgery, often followed by radiotherapy. However, there is a lack of evidence about how wide the surgical margin needs to be to minimise the risk of recurrence while preserving cosmetic outcomes.
In the US, guidelines recommend a minimum margin of 2 mm. In the UK, guidance has historically varied. In 2015, the ABS recommended 1 mm, while the National Institute of Health and Care Excellence advised 2 mm – both based on limited evidence.
Previous studies tended to rely on small, single-centre cohorts or on broad categories such as ‘clear’ versus ‘involved’ margins – referring to the absence or presence of cancer cells along the edge – rather than precise measurements taken from pathology reports.
Furthermore, randomising patients to either 1 vs 2 mm surgical margin widths in controlled trials to answer this question is neither practical or ethical due to the decision of which group would be the control – those given the standard of care – and those the experimental.
Using real-world data
To address this gap, the research team drew on prospectively collected national datasets, including NHS England cancer registration records, the ABS audit and the Sloane Project – an audit of screen-detected DCIS. The final analysis included 16,907 women aged 45 or over who were diagnosed with DCIS between 2003 and 2014 and treated with breast-conserving surgery.
By linking these datasets, the researchers were able to examine actual margin widths and relate them to long-term outcomes, including time to recurrence and overall survival.
Around 13 per cent of patients experienced a recurrence over the study period, and nearly 80 per cent of recurrences were invasive breast cancers rather than DCIS alone, which typically requires more intensive treatment. They found that women with margins under 2 mm had a increased risk of recurrence than those with margins of 2 mm or more, even after adjusting for factors such as age, tumour grade and size, use of radiotherapy and the number of previous surgeries.
Crucially, widening the margin beyond 2 mm did not appear to further reduce recurrence risk, suggesting there is a threshold above which additional margin width offers no further meaningful benefit.
The analysis also showed that undergoing multiple operations to achieve clear margins was itself associated with a higher risk of recurrence – a finding that has implications for discussions with patients about surgical options.
Changing guidance and practice
Last author Lucy Kilburn, Lead Statistician in the ICR-CTSU Breast and Rare Cancer Trials Group at The Institute of Cancer Research (ICR), said: “Our results have already had a tangible impact. Based on this dataset, the ABS has updated its guidance to recommend a minimum surgical margin of 2 mm for breast-conserving surgery in DCIS, bringing UK practice in line with US recommendations.
“The strength of our study lies in its scale and the quality of the data. By using real-world information from a national screening programme, we were able to answer a clinically important question that smaller studies could not resolve with confidence.”
Having evidence that reflects everyday practice rather than idealised trial conditions is important. In the absence of randomised trials, carefully analysed national audit data can play a critical role in shaping safe and effective standards of care.
Looking ahead
The research team says future work could involve analysing more recent cases, once follow has matured, to see whether the outcomes have sustained since the surgical guidance was updated by the ABS in 2014 – although this would depend on funding and approval for new data access.
Co-author, Professor Judith Bliss, Professor of Clinical Trials and Leader of the ICR-CTSU Breast and Rare Cancers Trials Group, said: “This study shows how national health data can directly inform and improve patient care. With greater access to routine health data becoming available we hope that we can enhance the quality and efficiency of clinical research studies, including clinical trials.”
