There is a lot of debate about whether the benefits of breast cancer screening outweigh the harms. Sir Michael Marmot estimated that Breast Cancer Screening in the UK saves 1,300 women’s lives every year. However, 70,000 women get false positive test results, which means the screening test (mammography) shows signs of cancer, but the test is wrong. This can make them feel anxious. Another 4,000 women receive unnecessary cancer treatment (overdiagnosis and overtreatment). This is because they have a cancer detected at screening that is so slow growing it never would have harmed her or given her any symptoms in her life. These are the best national estimates we have, but Sir Michael Marmot based his estimates on randomised controlled trials from the 1970s, using old tests and treatments.

International Variation in Breast Screening

Different countries give different versions of breast screening, because we are not sure which is best. In the UK we recall 4% of women for further tests because their mammograms show suspicious signs. Other countries recall as few as 2% (Denmark) or as many as 10% (USA). In the UK we offer screening every three years, which is the longest time between screens in the world. In the US it is every year or two years and in Europe every two years. Within England there is a lot of variability between centres, because we don’t know what is best to offer women. The research question: we are interested in finding out which version of breast screening gives most benefit and least harm. By version we mean how often women are invited, at what ages, and how many are recalled for further tests.

Our Approach

We need to understand which version of screening offers the most benefit with the least harm. To do this we need a very large study. We suggest making use of the data we already have. We have records from offering different versions of breast screening to over 13 million women in England over the last 25 years. This is called ‘retrospective observational research’, meaning we look back at the different versions of breast screening women were offered in the past, and see which versions gave most benefit and least harm.

The Research Plan

We will find the records for all women offered screening in England between 1990 and 2018. We will include information from the breast screening programme about what type of screening women had and when. We will add information about whether they got cancer and whether they died from the English Cancer Registry and Mortality and Births Information System. The benefits we will measure will include lives saved. The harms we measure will include numbers of false positive recalls, and overdiagnosed cases. We will also investigate how changes to number and type (grade, stage and size) of cancers detected at screening affect benefits and harms. We will explore how more or less detection of cell changes which look similar to cancer called Ductal Carcinoma in situ affect benefits and harms of screening.

Version 1.3 of the protocol can be accessed here and version 1.4 can be accessed here.

Patient and Public Involvement

Two breast cancer patients are part of the research team. With the support of Independent Cancer Patient Voices they have helped design the study, and will be involved at every stage.