Breast Screening and Over-diagnosis

Date: 29 October 2018

Women between the age of 50 and 70 (47 to 73 in some areas) 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 ‘over-diagnosis’ often crops up too. We discuss here what over-diagnosis means and what we think about it.

Firstly, what does over-diagnosis 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 been expressing concern about the ‘over-diagnosis’ of breast cancer. This describes a situation where some tumours are found during screening that would not have otherwise been detected. This is because these tumours are so slow growing, over that woman’s lifetime they wouldn’t have caused symptoms and wouldn’t actually cause harm if left untreated. 

What’s the problem?

The problem with over-diagnosis is that at the moment, it’s impossible to tell the difference between cancers that will kill and the cancers that won’t. So, to be on the safe side, 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 would receive, like surgery or chemotherapy, might be unnecessary. But currently, for any individual woman who is diagnosed with breast cancer through screening, doctors cannot be certain whether or not their breast cancer is one of the ‘over-diagnosed’ cancers that won’t cause harm, or one that is life-threatening. So 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 of course there’s still plenty that needs to be researched, such as this issue of over-diagnosis. 

What are the chances of this happening to me?

Although taking part in breast cancer screening is recommended by the NHS, it’s still up to you whether or not you want to attend. So, to help you in your decision, we’ve provided some numbers from a recent independent review of the UK breast screening programme, which provides the best estimate we currently have of the issue of over-diagnosis. 

For every 10,000 women invited for screening from aged 50 for 20 years:
•    681 women will be diagnosed with breast cancer over the course of 20 years – around 7%
•    Roughly 129 of these women will have been over-diagnosed, i.e. their cancer would have not otherwise been discovered nor would have been life threatening. 
•    43 deaths from breast cancer will be prevented, because of early diagnosis and treatment.

To put it another way, for any woman invited at the age of 50 to take part in the breast screening programme for 20 years, her chance of being ‘over-diagnosed’ 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 have never 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 to improve survival. However, with more sensitive tests there is a higher chance that they will pick up cancers that wouldn’t actually have caused any harm. So researchers are currently trying to find a balance between detecting cancers earlier but also making sure they pick up only the cancers that need treatment.

The more we support research to improve the screening programme, the better chance we have of fine-tuning screening processes and making sure that each woman receives the best individual treatment for her.

What Yorkshire Cancer Research advises 

The independent review of breast screening estimated that around 1,300 deaths from breast cancer are prevented every year because of the UK breast screening programme. However, breast screening results in 4,000 additional women being diagnosed who would have otherwise lived their lives without knowing they had breast cancer – but all of these ‘over-diagnosed’ women will survive their cancer.

Over-diagnosis 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 some more info about over-diagnosis 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. 

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