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There is much to commend about Australia’s lung cancer screening program, which started on July 1.

The program is based on gold-standard trial evidence showing this type of screening is likely to reduce lung cancer deaths.

Some people will have their life prolonged due to this screening, which involves taking low-dose CT scans to look for lung cancer in people with a significant smoking history.

In some of these people, cancer will be detected at an early stage, and they can be treated. Without screening, these people may have died of cancer because it would have been detected at a later, incurable stage.

However, for some people, screening could also harm.

How can screening harm?

Screening for disease, including cancer, can cause harm – during screening, diagnosis and treatment.

With lung cancer screening, a positive scan can prompt an invasive lung biopsy. This is where a sample of lung tissue is obtained with a special needle guided by imaging, or through surgery under anaesthesia.

If, after examination under the microscope, the pathologist thinks there is lung cancer, then more extensive surgery and other treatments will likely follow, all of which have a risk of side effects.

The diagnostic label “lung cancer” itself is distressing, and the stigma attached to the diagnosis may worsen this distress.

These harms and risks may be considered acceptable if the treatment prevents the person’s cancer from progressing.

However, as with other cancers, screening is likely to also cause overdiagnosis and overtreatment. That is, some of the lesions picked up through screening and diagnosed as cancer, would have never caused any trouble if they’d been left alone. If these lesions were left undetected (and untreated), they would never have caused symptoms or shortened the person’s life.

But all patients with a cancer diagnosis will be offered treatment – including surgery, radiotherapy and cancer drugs. Yet patients who really have an indolent (non-lethal) lesion have the same risk of harm from diagnosis and treatment as others, but without potentially benefiting from treatment.

A related issue is that of “incidental findings”. Reports from lung cancer screening programs overseas show there is a large potential to find things other than cancer on the CT scan.

For instance, some people have lung “nodules” (small spots on the scan) that fall short of being suspicious for cancer, but nonetheless need close monitoring with repeat scans for a while. For these people, we need to make sure health-care workers follow protocols that prevent unnecessary intervention in a nodule that is not growing.

The scans can also pick up other conditions. These include calcium in coronary arteries, small aneurysms of the aorta (bulges in the body’s largest artery), or abnormalities in abdominal organs such as the liver.

Some of these “incidental findings” may lead to early detection of disease that can be treated. However, in many cases the findings would not have caused any issues if they’d been left undetected, another example of overdiagnosis. These patients experience risks from further cascades of interventions triggered by the incidental finding, but without these interventions improving their health.

The potential for overdiagnosis and overtreatment is greater if screening extends beyond the high-risk group with a history of heavy smoking. Some people who don’t meet the eligibility criteria may still want to be screened. For example, lung cancer awareness campaigns may lead to people who don’t smoke requesting screening. If screening staff decide to refer them for imaging, this may result in unofficial “leakage” of the screening program to include people at lower risk of cancer.

For example in the United States, an estimated 45% of scans done in its screening program are for people who do not meet eligibility criteria. In China, about 64% of those screened may be technically ineligible.

We see the results of this in a number of Asian countries with widespread, non-targeted screening, including of people who do not smoke. This has resulted in high rates of cancer diagnosis – much higher than we would expect in this low-risk group – and even higher rates of lung surgeries.

These surgeries, which involve cutting into the chest wall to remove lung tissue, carry significant operative risks. They may also cause longer-term impacts by removing normal lung tissue.

Regular independent evaluation needed

In Australia, for the eligible population with a significant smoking history, we anticipate net benefit, on balance, from the screening program.

However, if unintended consequences from screening are higher in real life than in the trials, then this could tip it the other way into net harm.

So, regular independent re-evaluation of the program is needed to ensure anticipated benefits are realised and harms are kept to a minimum.

This should include analysis of data across the population to look for signs of benefit, such as decreases in rates of advanced-stage lung cancer and deaths.

These data should also be scrutinised for signs of harm from overdiagnosis and overtreatment – including of both cancer and non-cancer conditions.

There is much excitement about the potential for lung cancer screening to prevent some Australians from dying from this devastating disease. We too have cautious optimism the program could make a real difference.

But we can’t let this optimism blind us to the potential for harm.

This is the next article in our ‘Finding lung cancer’ series, which explores Australia’s first new cancer screening program in almost 20 years. Read other articles in the series.

More information about the program is available. If you need support to quit smoking, call Quitline on 13 78 48.