Breast screening programme shows benefit of detecting very early cancers
New research from Professor Stephen Duffy’s research team shows that invasive breast cancer can be prevented by screening for and treating an earlier form called ductal carcinoma in situ (DCIS).
The study, published in Lancet Oncology, is the first to explicitly investigate the association between screen-detection of DCIS and subsequent incidence of invasive breast cancer within the NHS Breast Screening Programme.
DCIS is considered a precursor to breast cancer, where abnormal cells are present in milk ducts in the breast, but have not yet invaded the surrounding tissue. Around 4,800 people are diagnosed with DCIS in the UK each year and the preferred treatment is currently surgery followed by radiotherapy.
Ongoing public debate about the harm caused by mammography screening through overdiagnosis has led to controversy over the value of screening for and treatment of DCIS. A major question has been the extent to which diagnosis and treatment of DCIS may prevent the occurrence of invasive breast cancer in the future.
What have we found?
Our researchers analysed data from 5,243,658 women aged 50-64 who were screened over a four year period across 84 screening units in the NHS Breast Screening Programme in England, Wales and Northern Ireland.
They found that increased prior screen detection of DCIS correlated with a reduction in invasive cancer cases over the next three years. In 90 per cent of the screening units, for every three screen-detected cases of DCIS, there was one fewer case of invasive cancer in the following three years. As the study is based on anonymised screening unit level data, it cannot give definitive proof of progressive potential or otherwise of individual DCIS cases.
As study lead, Professor Duffy said:
“There has been controversy over whether ductal carcinoma in situ will ever become invasive cancer. This is the first study from the screening programme which suggests that a substantial proportion of DCIS will become invasive if untreated, and it is therefore worth detecting and treating early.
“People can be reassured that detection of DCIS in the breast screening programme is benefitting the patients.”
The findings suggest that, overall, detection and treatment of DCIS is worthwhile in the prevention of subsequent invasive disease. The authors note, however, that it cannot be known for certain what the outcome would have been for any individual with DCIS if they had not been treated.
The average rate of DCIS detected at screening was 1.6 per 1,000 women screened, while the subsequent average rate of invasive cancers found within 36 months of their last screen was 2.9 per 1,000 screened.
Breast cancer progression: the transformation of normal breast ducts (left) to ductal carcinoma in situ (DCIS) and invasive cancer (right). Myoepithelial cells are shown in the stained tissue images (upper panels) in brown. These cells surround the epithelial duct cells (represented in navy blue in the lower diagrams).
In DCIS the lumen (central space inside the duct) becomes filled with precancerous and cancerous cells. Sometimes this condition will progress and tumour cells break out of the duct, invading the surrounding tissue. Image from Allen et al. 2013 Clin Cancer Res.
The research was funded by the Department of Health Policy Research Programme and NHS Cancer Screening Programmes.
Screen detection of ductal carcinoma in situ and subsequent incidence of invasive interval breast cancers: a retrospective population-based study
Duffy, SW, Dibden A, Michalopoulos D, Offman J, Parmar D, Jenkins J, Collins B, Robson T, Scorfield S, Green K, Hall C, Liao X, Ryan M, Johnson F, Stevens G, Kearins O, Sellars S, Patnick J. The Lancet Oncology, 3 December 2015.
Western Daily Press - Breast cancer screening for an 'early form' will help 5000 women a year, says study
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Breast Cancer Progression – Can We Predict It? Barts Cancer Institute
With thanks to Marianne Baker