Breast screening and overdiagnosis

Date: 29 October 2018

Women between the age of 50 and 70 are invited for breast screening every three years, with the aim of detecting cancers at the earliest stage when they are most treatable. But when breast screening is discussed in the news, the term ‘overdiagnosis’ can sometimes crop up too.

Firstly, what does overdiagnosis mean?

All cancers are different; some tumours are aggressive and grow very fast, causing damage to the body and threatening life. Others are much slower growing and may not cause as much harm. 

In recent years, some people in the healthcare community have expressed concern about the ‘overdiagnosis’ of breast cancer. This describes a situation where some tumours are found during breast screening that would not have otherwise been detected. This is because these tumours are so slow growing over the woman’s lifetime that wouldn’t have caused symptoms or proved harmful if left untreated.

What’s the problem?

The problem with overdiagnosis is that it’s currently impossible to tell the difference between cancers that can kill and those that won’t. When someone is diagnosed with breast cancer, doctors will recommend treatment without knowing for certain whether the cancer would go on to cause harm or not.

Understandably, nobody wants to receive a cancer diagnosis and all the worry and uncertainty that can bring. Equally, it’s not nice to think that the treatment you receive, like surgery or chemotherapy, might be unnecessary. For now, scientists agree it’s better to be safe than sorry when it comes to breast cancer.

There have been some breath-taking scientific achievements when it comes to breast cancer diagnosis and treatment in the last couple of decades, but there’s still plenty that needs to be researched, such as the issue of overdiagnosis.

What are the chances of this happening to me?

Taking part in breast cancer screening is recommended by the NHS, but it’s up to you whether or not you want to attend. To help you in your decision, here are some numbers taken from an independent review of the UK breast screening programme. They provide the best estimates we currently have. 

For every 10,000 women invited for screening from aged 50 for 20 years:

•    681 women (around 7%) will be diagnosed with breast cancer over the course of 20 years.
•    Roughly 129 of these 681 women will have been overdiagnosed, i.e. the cancer that has been found would not have proved life threatening if it had not been discovered. 
•    However, 43 of the 681 women will live because of the early diagnosis and treatment of their cancer.

To put it another way, for any 50-year-old woman invited to take part in the breast screening programme for 20 years, the chance of being ‘overdiagnosed’ with breast cancer is roughly 1%.

For every breast cancer death prevented by the screening programme, around three women will be diagnosed with breast cancer that would never have become life-threatening.

What’s being done about over-diagnosis?

Researchers are constantly trying to find new technology to improve screening and diagnose cancer earlier. In the future, the breast screening programme may undergo changes based on new evidence and research. An option being explored across different screening programmes is ‘risk-stratification’, which involves screening people at high risk more than those at low risk (or screening them in a different way).

The more we support research to improve the screening programme, the more likely we are to fine-tune screening processes and make sure that each woman receives the best individual treatment for her.

What Yorkshire Cancer Research advises 

Overdiagnosis can seem like a very complicated idea, especially if you’re being invited to the breast cancer screening programme for the first time. But on balance, we strongly encourage all women to attend breast screening when invited. Getting screened regularly could save your life.

Got more questions?

If you would like more information about overdiagnosis or anything to do with breast screening, the NHS breast screening programme provides some guides which can help. Alternatively, you can make an appointment to chat with your GP, or contact your local breast screening unit, before making your decision. 

This content of this article was reviewed and updated in October 2020.

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