Screening for and treatment of ductal carcinoma in situ (DCIS) is found to prevent subsequent invasive cancer, according to research published in Lancet Oncology (doi:10.1016/S1470-2045(15)00446-5).

DCIS is described as an early form of breast cancer; cancer cells are present in milk ducts but have not yet invaded surrounding breast tissue. DCIS is diagnosed in approximately 49 000 people in the United States each year. Standard treatment is surgery followed by radiotherapy.

Ongoing debate on the harms of overdiagnosis has led to controversy over the value of screening for and treatment of DCIS. A major question is the extent to which diagnosis and treatment of DCIS may prevent invasive breast cancer in the future.

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The researchers, led by Queen Mary University of London (QMUL) in the United Kingdom, analyzed data on 5 243 658 women age 50 to 64 years who were screened over a 4-year period across 84 screening units in the UK  National Health Service Breast Screening Programme in England, Wales, and Northern Ireland.

They found that increased screen detection of DCIS was associated with a reduction in invasive cancers during the subsequent 3-year interval. In 90% of the screening units, for every 3 screen-detected cases of DCIS, there was 1 fewer case of invasive cancer in the following 3 years. The study is based on screening unit level data; therefore, it cannot give definitive proof of progressive potential or otherwise of individual DCIS cases.

“There has been controversy over whether ductal carcinoma in situ will ever become invasive cancer. This is the first study from the screening program 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 program is benefitting the patients,” said lead researcher Professor Stephen Duffy at QMUL.

This study 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.

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 patient with DCIS if the patient had not been treated.

The average rate of detection at screening was 1.6 cases of DCIS per 1000 women screened, while the subsequent average rate of invasive cancers found within 36 months of their last screen was 2.9 cases of invasive cancer per 1000 screened.

The research was funded by the Department of Health Policy Research Programme and NHS Cancer Screening Programmes.