Lung cancer screening reveals hidden abnormalities

4 minute read

CT scans show that 33% of heavy smokers have significant incidental findings, US data shows.

One in three current or former heavy smokers who had low-dose computed tomography screening had at least one abnormality that was not associated with cancer, according to new research.

As Australia is set to launch a national lung cancer screening program in July 2025, US data shows that CT screening detected problems that would not have been found until participants developed symptoms at a later point, such as more advanced emphysema or later stage cancer.

The US researchers found that of the significant incidental findings, 89% were abnormalities that needed to be reported to the referring doctor for follow-up.

“This represented a substantial number of findings for which further evaluation was likely needed,” they wrote in JAMA Internal Medicine.

“At the same time, it may also represent an opportunity for early intervention for clinically important extrapulmonary cancers, cardiovascular, and respiratory conditions.”

The more than 26,000 participants had a history of heavy smoking – at least 30 pack years – and were screened with low-dose computed tomography as part of the US’s lung cancer screening trial.

The researchers defined “significant incident findings” as a negative screen result with significant abnormalities that were not suspicious for lung cancer, or a positive screen result with emphysema, significant cardiovascular abnormality, or significant abnormality above or below the diaphragm.

The most common significant incidental findings were emphysema (43% of all findings), coronary artery calcium (12%), and masses or suspicious lesions (7%). Masses commonly included kidney, liver, adrenal and breast abnormalities.

The researchers used data from the National Lung Screening Trial, which included more than 53,000 participants aged 55 to 74 with a smoking history of 30 pack years who were either currently smoking or had quit within the previous 15 years.

The US participants were randomly assigned to have either low-dose computed tomography or chest X-rays at baseline, and then had two more follow-up screens at one-year intervals, and were followed up for five to seven years.

The researchers found that there was a higher proportion of reportable significant incidental findings among participants with a positive screen result for lung cancer (94.1%) compared with those with a negative screen result (81.8%).

“Significant incidental findings were more common in participants with a screening result that was positive for lung cancer (44.7%) than for participants with a negative screen result for lung cancer (9.9%),” they said.

“However, given the many participants with a negative LDCT screen result for lung cancer (56,985 at 3 screening examinations), this is a substantial number of potentially clinically significant findings (5620).”

Lead author and epidemiologist Associate Professor Ilana Gareen from Brown University said they weren’t especially surprised that one third of participants had significant incidental findings, because they all had a history of heavy smoking.

Professor Brown told Oncology Republic that many of the participants may have been diagnosed with these issues without screening, but only at a later point once symptoms had developed.

“According to the literature, many of them would not be diagnosed until they became symptomatic; that is, with more advanced emphysema or later stage cancer. 

“For some participants, the findings were ‘incidentalomas’ and would never be diagnosed.”

Professor Gareen said they had data on the participants who had X-ray screening and planned to report that in a future paper.

The researchers will compare mortality in the low-dose computed tomography and chest X-ray (CXR) arms of the study as it relates to significant incidental findings (SIFs), she said. 

“There were many fewer SIFs in the CXR arm of the study due to the lower resolution of CXR.”

Professor Gareen said they anticipate that some of the significant incidental findings will indicate potential future cancers. “We are currently working on a paper exploring this issue,” she said.

“SIFs are an important issue in lung screening, and in all imaging.

“The discovery of a SIF offers the opportunity to diagnose pathological conditions early, but it also carries the risk of unnecessary medical interventions. 

“It is important that evidence-based standardised approaches to reporting and evaluating these SIFs are developed.”

Professor Gareen said lung cancer screen has been shown to reduce lung cancer mortality, but patients and medical providers must be aware of the high likelihood of detecting significant incidental findings, which must be appropriately reported and managed.

Australia’s future screening program will target high-risk individuals to detect lung cancer, which killed more than 8600 Australians in 2022. Patients will be eligible if they’re aged 50 to 70, are asymptomatic, have a history of tobacco smoking of at least 30 pack-years, and if a former smoker, have quit within the past 10 years.

JAMA Internal Medicine 2023, online 8 May

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