Overdiagnosis

What is overdiagnosis?

Overdiagnosis is the diagnosis of a cancer that wouldn’t have gone on to cause harm in a person’s lifetime. In other words, if the person hadn’t been tested (whether that’s via screening or some other type of test), they might never have known that they had cancer and would not have died from the disease. It’s a complex issue that’s important to understand at a population level but difficult to predict at an individual level. 

How does overdiagnosis happen?

Not all cancers behave in the same way. This is true even for cancers starting in the same part of the body. Some will spread quickly, whilst others are very slow-growing and will never be the cause of someone dying.  

It’s when these slower-growing cancers are picked up that they’re said to be over diagnosed. This is more common in some cancer types than others. The likelihood of overdiagnosis is also influenced by the frequency of diagnostic examinations or screening, the ability of the tests to detect small irregularities, and the threshold to label these as cancer¹

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When does overdiagnosis occur in practice?

Breast screening picks up early-stage cancers that are more likely to be treated successfully. But it also comes with potential trouble, including overdiagnosis; this is because some early invasive breast cancers wouldn’t have gone on to cause the patient harm. Research has shown that for each woman whose life is saved through breast screening, around three will be diagnosed with a breast cancer that would have never caused harm or death²

. It’s therefore important that women have this information so they can make a fully informed decision about whether or not to go for screening.

Prostate specific antigen (PSA) testing is another example that can result in overdiagnosis of prostate cancer. PSA is a protein made by the prostate and detected in blood samples. A man’s PSA level can be raised for many reasons, including an enlarged prostate, infection and prostate cancer. Research has shown that using the PSA test in men with no symptoms can result in more harm than good, including the potential for unnecessary investigations, overdiagnosis, and over-treatment³

.  It’s important that health professionals counsel people on the benefits and limitations of the PSA test, so they can make an informed decision on taking it.. Read our Recognition and referral of suspected prostate cancer guide for further guidance.  

Why is overdiagnosis important?

It’s important for health professionals to be aware of overdiagnosis and able to explain this to patients when appropriate, for example when supporting someone to make an informed choice on whether to take part in cancer screening. You may wish to direct patients to our information on the benefits and harms of cancer screening for the general public.  

Most people diagnosed with cancer do receive some form of treatment. This means some who are overdiagnoesd will go through treatment, distress and potential side effects when they didn’t need to. This is because it’s not yet possible to tell at the point of finding a cancer whether it could go on to cause harm or death if left untreated. There’s a lot of research underway to see if it might be possible to better identify which cancers need treating, and which ones don’t. See a more in-depth discussion on overdiagnosis on our blog linked below.

Read our blog on overdiagnosis