What is overdiagnosis?

It is important to know that overdiagnosis isn't the same as misdiagnosis. Misdiagnosis is a wrong diagnosis – for instance, if someone is diagnosed with cancer but they actually have a benign cyst. Overdiagnosis, on the other hand, is a “correct” medical diagnosis.

Overdiagnosis is also not the same as a false alarm. By this we mean abnormal findings, for instance seen in an x-ray, which further tests show to be harmless. The medical term for this is a false-positive result.

Most screening tests can lead to cases of overdiagnosis. This is well documented in the area of breast cancer screening and prostate cancer screening.

Studies on these two types of screening have shown that they can lead to overdiagnosis. The studies involved more than 10,000 women and men who were followed up for many years. Half of the participants were screened for cancer, and the other half weren't. Because the groups of participants were similar otherwise, you would expect a similar number of people in each group to develop cancer over time. The researchers kept track of how many people in the two groups developed cancer over a number of years, and compared the groups. The outcome: Considerably more people in the screening group were diagnosed with cancer. The studies on breast cancer screening, for instance, showed that about 2 out of 10 people who were diagnosed with breast cancer would never have noticed that they had a tumor if it hadn't been discovered through screening. The same may be true for up to 3 out of 10 people whose prostate cancer was discovered after they had a PSA test.

All screening tests can potentially result in overdiagnosis. This is of particular significance when it comes to cancer because a wide variety of cancer screening tests are offered. Also, it’s often impossible to accurately predict how a tumor will develop, especially in the early stages of cancer when it's small. Tumors don't always grow a lot and become life-threatening. They may develop in one of the following ways instead:

• The tumor may grow, but so slowly that the person dies of something else before the tumor starts causing symptoms.
• The tumor may not grow at all, or even disappear again on its own. Then the person may live a long life without ever knowing that they had cancer.

We know that some tumors don't grow, or only grow slowly, from studies in which autopsies were performed on elderly women and men who died of something else. For example, in some studies researchers took a very close look at the prostates of men who had died. The outcome: about 3 out of 10 men between the ages of 60 and 70 had a small prostate cancer tumor that they never knew about.

The consequences of overdiagnosis will largely depend on the medical condition in question: If screening leads to the discovery of a disease that doesn't appear to be very serious and is easy to treat, then overdiagnosis is harmless. But things are different if screening leads to the discovery of a disease like cancer. Then the diagnosis itself can already be very hard to cope with, having a major impact on your life.

If cancer is discovered through screening, it's generally impossible to know whether that person’s diagnosis is a case of overdiagnosis. So screening may lead to unnecessary treatments (“overtreatment”). Those treatments, such as surgery, are also distressing and sometimes associated with risks.

Picture a woman named Andrea. She is 65 years old and has a small, very slow-growing tumor in her breast. She doesn’t know about it. At the age of 77 she dies of a heart attack – not breast cancer.

If she had gone for screening at the age of 65, she would have been diagnosed with breast cancer and faced a lot of psychological stress and unpleasant treatments. She and her treatment team would then have believed that her tumor had been successfully “cured.” She wouldn’t actually have lived longer, though. But being a cancer patient would have greatly affected her wellbeing and quality of life.

Overdiagnosis isn’t only an issue when it comes to cancer screening. Other examples include bulges in weak blood vessels (aneurysms) and abnormal-looking spinal discs. Some medical conditions are discovered purely by chance – for instance when doing tests for an unrelated medical problem. Routine check-ups may also lead to the discovery of abnormal readings or changes in tissue. It is hard to know how often we are “ill” and get better again without ever realizing it.

Overdiagnosis would be significantly less of a problem if we could accurately predict the course of the disease that is diagnosed. Despite researchers’ efforts, reliable predictions aren't yet possible. With some illnesses, though, people can decide to wait and see what happens rather than starting treatment. For instance, after being thoroughly informed, some men with early-stage prostate cancer are prepared not to start treatment, and instead wait and see whether or how their tumor develops in the months and years that follow.

People who would like to avoid overdiagnosis at all costs would also have to avoid all types of screening.

Because some screening tests also have benefits, it’s worth finding out all about the screening test you are considering, and carefully thinking about the pros and cons. You may end up deciding to have one screening test, but not another. Screening tests are never urgent. There’s always enough time to get hold of information and think things over.

One important aspect is whether the screening test has even been proven to have any positive effects. Many of the screening tests offered in doctors’ practices and hospitals haven’t been proven to do so. So people who decide to have those screening tests enter risks without knowing whether there are any benefits.

Carefully considering the benefits and drawbacks of screening tests can help you reach the best decision for you:

• Would you rather have regular screening tests, even if that means risking overdiagnosis, with all the physical and psychological consequences?
• Or would you prefer to avoid unnecessary diagnoses and treatments – even if that means that a serious illness might only be discovered at a later stage, when treatment may be less effective?

Many people find it hard to make this kind of decision. It is important to carefully consider the pros and cons. Talk things over with the people you are close to, and don't hesitate to ask other doctors about the potential advantages and disadvantages of the screening test.